                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  No. 04-10226
                Plaintiff-Appellee,
               v.                            D.C. No.
                                          CR-03-00062-1-HG
DANIEL KUUALOHA AUKAI,
                                              OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
                for the District of Hawaii
         Helen Gillmor, District Judge, Presiding

                 Argued and Submitted
             May 11, 2005—Honolulu, Hawaii

                   Filed March 17, 2006

  Before: Dorothy W. Nelson, Consuelo M. Callahan, and
              Carlos T. Bea, Circuit Judges.

                   Opinion by Judge Bea




                           2837
2840                UNITED STATES v. AUKAI


                         COUNSEL

Edward H. Kubo, Jr., United States Attorney for the District
of Hawaii, and Thomas J. Brady, Assistant United States
Attorney for the District of Hawaii, for plaintiff-appellee the
United States of America.

Pamela O’Leary Tower, Honolulu, Hawaii, for defendant-
appellant Daniel Kuualoha Aukai.
                    UNITED STATES v. AUKAI                  2841
                          OPINION

BEA, Circuit Judge:

   We must decide whether a prospective commercial airline
passenger, who presented no identification at check-in, and
who voluntarily walked through a metal detector without set-
ting off an alarm, can then prevent a government-ordered sec-
ondary screening search by stating he has decided not to fly
and wants to leave the terminal. We hold that such passenger
cannot prevent the secondary search because such search
comports with the Fourth Amendment’s requirement that a
search be reasonable where, as here, the initial screening was
“inconclusive” as defined in United States v. Torbet, 298 F.3d
1087, 1089-90 (9th Cir. 2002). We need not and therefore do
not decide whether the same would be true were the second-
ary screening more intrusive or were it triggered by the sub-
jective evaluation of the prospective passenger by airline or
security personnel rather than more objective criteria such as
a screening machine alarm being triggered, random selection,
or, as here, the prospective passenger’s failure to present iden-
tification upon checking in.

                               I.

                               A.

   On February 1, 2003, Defendant-Appellant Daniel Kuu-
aloha Aukai arrived at the Honolulu International Airport
intending to take a Hawaiian Airlines flight from Honolulu,
Hawaii to Kona, Hawaii. He proceeded to check in at the
ticket counter, but did not produce a government-issued pic-
ture identification. Accordingly, the ticket agent wrote the
phrase “No ID” on Aukai’s boarding pass.

   Aukai then proceeded to the security checkpoint, where
signs were posted advising prospective passengers that they
and their carry-on baggage were subject to search. He entered
2842                UNITED STATES v. AUKAI
the security checkpoint at approximately 9:00 a.m., placed his
shoes and a few other items into a plastic bin, and then volun-
tarily walked through the metal detector or magnetometer.
The parties agree that the magnetometer did not signal the
presence of metal as Aukai walked through it. Nor did his
belongings trigger an alarm or otherwise raise suspicion as
they passed through the x-ray machine. After walking through
the magnetometer, Aukai presented his boarding pass to
Transportation Security Administration (“TSA”) Officer Cor-
rine Motonaga.

   Pursuant to TSA procedures, a passenger who presents a
boarding pass on which “No ID” has been written is subject
to secondary screening even if he or she has passed through
the initial screening without triggering an alarm or otherwise
raising suspicion. As it was performed here, secondary
screening consists of a TSA officer passing a handheld mag-
netometer, known as a “wand,” near and around the passen-
ger’s body. If the wand detects metal, it sounds an alarm. The
TSA officer then discerns the cause of the alarm, using tech-
niques such as feeling the outside of the passenger’s clothes
in the area that caused the alarm and, if that area is near a
pocket, directing the passenger to empty his pocket.

   Because Aukai’s boarding pass had the “No ID” notation,
Motonaga directed Aukai to a nearby, roped-off area for sec-
ondary screening. Aukai initially complied, but complained
that he was in a hurry to catch his flight, which, according to
the boarding pass, was scheduled to leave at 9:05 a.m.
Although Aukai went to the roped-off area as directed, he did
not stay there. When Motonaga noticed that Aukai had left the
area and was gathering his belongings from the plastic bin,
she instructed Aukai that he was not allowed to retrieve his
property and that he had to stay in the roped-off area.

  Aukai then appealed to TSA Officer Andrew Misajon, who
was to perform the secondary screening, explaining again that
he was in a hurry to catch his flight. Misajon nonetheless had
                    UNITED STATES v. AUKAI                2843
Aukai sit in a chair, and thereafter proceeded to use the wand
to detect metal objects. At some point, Misajon had Aukai
stand, and when Misajon passed the wand across the front of
Aukai’s body, the wand alarm was triggered at Aukai’s front
right pants pocket. Misajon asked Aukai if he had anything in
his pocket, and Aukai responded that he did not. Misajon
passed the wand over the pocket a second time; again the
wand alarm was triggered. Misajon again inquired whether
Aukai had anything in his pocket; again Aukai said he did not.
Misajon then felt the outside of Aukai’s pocket and concluded
that something was inside the pocket. Misajon could also see
the outline of an unknown object in Aukai’s pocket. At some
point during this screening process, Aukai informed Misajon
that he wanted to leave the airport.

   At this point, TSA Supervisor Joseph Vizcarra approached
Misajon and asked whether he needed assistance. Misajon
related the events; Vizcarra asked Misajon to pass the wand
over Aukai’s pocket again. When the wand alarm again was
triggered, Vizcarra directed Aukai to empty his pocket. Aukai
again protested that he had nothing in his pocket. Using the
back of his hand, Vizcarra touched the outside of Aukai’s
pocket and felt something in the pocket. He again directed
Aukai to empty his pocket. This time Aukai reached into his
pocket and removed either his keys or change, but a bulge
was still visible in his pocket. Vizcarra directed Aukai to
remove all contents from his pocket. After claiming at first
that there was nothing more, Aukai finally removed an object
wrapped in some form of tissue paper and placed it on a tray
in front of him.

  Suspecting that the item might be a weapon, Vizcarra sum-
moned a nearby law enforcement officer. Vizcarra then
unwrapped it and discovered a glass pipe used to smoke
methamphetamine. The law enforcement officer took control
and escorted Aukai to a small office near the security check-
point. Aukai was placed under arrest and was searched inci-
dent to his arrest. During the search, the police discovered in
2844                UNITED STATES v. AUKAI
Aukai’s front pants pockets several transparent bags contain-
ing a white crystal substance. Aukai eventually was taken into
federal custody, where he was advised of and waived his
Miranda rights, and then gave a statement in which he incul-
pated himself in the possession of methamphetamine.

                               B.

   Five days later, Aukai was indicted for knowingly and
intentionally possessing, with the intent to distribute, 50
grams or more of methamphetamine, its salts, isomers, and
salts of its isomers, a Schedule II controlled substance, in vio-
lation of 21 U.S.C. §§ 841(a), 841(b)(1)(A)(viii). Aukai filed
a motion to suppress the evidence found incident to his arrest
at the airport and the statement he later made, which motion
the district court denied. Aukai then pleaded guilty pursuant
to a written plea agreement that preserved his right to appeal
the denial of his suppression motion. The district court sen-
tenced Aukai to a term of imprisonment of 70 months and a
term of supervised release of 5 years, and Aukai timely
appealed. We have jurisdiction pursuant to 28 U.S.C. § 1291,
and affirm Aukai’s conviction.

                               II.

  We review de novo the district court’s legal basis for deny-
ing a motion to suppress, but review the district court’s find-
ings of fact for clear error. United States v. Marquez, 410
F.3d 612, 615 (9th Cir. 2005), as amended by 2005 WL
1661572 (9th Cir. July 18, 2005).

                              III.

   [1] Federal law mandates that commercial airlines must
refuse to transport any prospective passengers who do not
submit to a search of their persons and possessions for dan-
gerous weapons, explosives and other destructive devices
prior to boarding an aircraft. 49 U.S.C. § 44902. In United
                         UNITED STATES v. AUKAI                          2845
States v. Davis, 482 F.2d 893 (9th Cir. 1973), we held that
such “nationwide anti-hijacking program[s,] conceived,
directed, and implemented by federal officials in cooperation
with air carriers,” are not “beyond the reach of the Fourth
Amendment.” Id. at 897. Nevertheless, we deemed these air-
port security screenings “administrative” searches to the
extent that they are “conducted as part of a general regulatory
scheme in furtherance of an administrative purpose, namely,
to prevent the carrying of weapons or explosives aboard air-
craft, and thereby to prevent hijackings,” “rather than as part
of a criminal investigation to secure evidence of crime.” Id.
at 908. We held that, as “administrative” searches, airport
security screenings are “permissible under the Fourth Amend-
ment though not supported by a showing of probable cause
directed to a particular place or person,” id., if, despite the
absence of a warrant, they nonetheless “meet the Fourth
Amendment’s standard of reasonableness.” Id. at 910. Finally,
we concluded that an airport security screening process satis-
fies this reasonableness standard provided “[1] that [it] is no
more extensive nor intensive than necessary, in the light of
current technology, to detect the presence of weapons or
explosives, [2] that it is confined in good faith to that purpose,
and [3] that potential passengers may avoid the search by
electing not to fly.” Id. at 913.

   At issue here is only the third element of the Davis test:
“[T]hat potential passengers may avoid the search by electing
not to fly.” Id. at 913; accord id. at 910-11 (“It follows that
airport screening searches are valid only if they recognize the
right of a person to avoid search by electing not to board the
aircraft.”); id. at 912 (“In sum, airport screening searches of
the persons and immediate possessions of potential passen-
gers for weapons and explosives are reasonable under the
Fourth Amendment provided each prospective passenger
retains the right to leave rather than submit to the search.”).1,
  1
   Aukai does not otherwise contest the lawfulness of the screening nor
of his subsequent arrest and the search incident to that arrest. In particular,
2846                    UNITED STATES v. AUKAI
2
    In this regard, Aukai does not contest that he impliedly con-

Aukai does not contend that his secondary screening violated either of the
Davis test’s two other necessary elements: that the screening was “no
more extensive nor intensive than necessary, in the light of current tech-
nology, to detect the presence of weapons or explosives,” and that it was
“confined in good faith to that purpose.”
   Regarding the former element involving the intrusiveness of the screen-
ing, Aukai does not contest the fact that he was not wanded after he had
removed his keys or change from his pocket and before being ordered to
remove from his pocket whatever it was that caused the visible and palpa-
ble bulge. See United States v. Pulido-Baquerizo, 800 F.2d 899, 901-02
(9th Cir. 1986) (holding that “a visual inspection and limited hand search
of luggage” that “is conducted in a manner which produces negligible
social stigma” “involves only a slight privacy intrusion”).
   Regarding the latter element involving the screening’s good faith limita-
tion to its administrative purpose, Aukai does not contest that the screen-
ing was triggered by the objective criterion that he failed to present
identification upon his checking in at the airport. Therefore, this opinion
does not decide whether a secondary screening triggered solely by arbi-
trary and subjective criteria would be “confined in good faith to [detect the
presence of weapons or explosives],” and hence, a reasonable search under
the Fourth Amendment. See United States v. Henry, 615 F.2d 1223, 1228
(9th Cir. 1980) (reasoning that the non-discriminatory and objective nature
of the airport screening in question supported a finding that the screening
was “reasonable” apart and distinct from another necessary element of the
Davis test that the passenger impliedly consented to the screening); Davis,
482 F.2d at 910, 911 & n.51 (reasoning that an airport search was similar
to other administrative searches that did not require a warrant because it
was “ ‘not subject to the discretion of the official in the field,’ ” but also
requiring that passengers impliedly consent to such searches (quoting
Camara v. Municipal Court, 387 U.S. 523, 532 (1967)).
   2
     Although the third element of the Davis test speaks of “electing” not
to fly rather than “consenting” to the search, we recognized in Davis that
the two are opposite sides of the same coin:
     We have held that, as a matter of constitutional law, a prospective
     passenger has a choice: he may submit to a search of his person
     and immediate possessions as a condition to boarding; or he may
     turn around and leave. If he chooses to proceed, that choice,
     whether viewed as a relinquishment of an option to leave or an
     election to submit to the search, is essentially a “consent,” grant-
     ing the government a license to do what it would otherwise be
     barred from doing by the Fourth Amendment.
                        UNITED STATES v. AUKAI                          2847
sented to the initial metal detector screening and that such
screening complied with the third element of the Davis test.3
Instead, he argues that the secondary screening violated the
third element of the Davis test because, following his implied
consent to the initial screening, he elected not to fly rather
than undergo the secondary screening and, thereby, revoked
his implied consent. As noted above, the district court found
that Aukai informed Misajon that he wanted to leave the air-
port only “[a]t some point” during the secondary screening,
but before the methamphetamine pipe was discovered.
Indeed, the testimony from the hearing on Aukai’s motion to
suppress does not evince when Aukai declared his intent to
leave the airport. Nevertheless, we assume, as Aukai repre-
sents and as the government concedes, that Aukai declared his
election not to fly and his desire to leave the airport before the
wanding procedure.4 Our task, to which we now turn, is to
determine whether that election was valid.

Davis, 482 F.2d at 913 (emphasis added); accord Henry, 615 F.2d at 1228
(9th Cir. 1980) (“We have interpreted Davis to require that the search be
reasonable and that there be ‘implied consent’ by the person to be
searched.”) (citing McMorris v. Alioto, 567 F.2d 897, 900 (9th Cir.
1978)); United States v. Homburg, 546 F.2d 1350, 1352 (9th Cir. 1976)
(“In [Davis], we held that the justification for warrantless screening
searches is the implied consent of the passenger.”).
   3
     Nor could he. See Marquez, 410 F.3d at 617-18 (“In this case, Marquez
checked in, went to the security checkpoint, waited in line, placed his bag
on the x-ray scanner, proceeded through the walkthrough magnetometer,
and allowed [the TSA officer] to begin screening his person with the hand-
held magnetometer; he had ample opportunity to choose to forego air
travel in order to avoid the screening.”); Davis, 482 F.2d at 914 (“It may
well be that under the present airport screening program, operating pursu-
ant to current regulations, the alternatives presented to a potential passen-
ger approaching the screening area are so self-evident that his election to
attempt to board necessarily manifests acquiescence in the initiation of the
screening process.”).
   4
     We note that after the wanding procedure began, Aukai claimed not to
have anything in his pockets on at least three occasions despite the wand
alarm having been triggered and, indeed, despite an obvious bulge in his
pocket. However, because this occurred after Aukai’s stated intention to
leave the airport, we do not address whether this behavior may have been
sufficiently suspicious to itself warrant at least a Terry stop-and-frisk. See
Terry v. Ohio, 392 U.S. 1, 27-30 (1968).
2848                   UNITED STATES v. AUKAI
                                   A.

   [2] Although we held in Davis that “airport screening
searches are valid only if they recognize the right of a person
to avoid [the] search by electing not to board the aircraft,” 482
F.2d at 910-11, we did not address when such a choice must
be made—that is, whether there is some stage during or after
which a prospective passenger may not withdraw his implied
consent to a search of his person or carry-on baggage by
electing not to fly. Pulido-Baquerizo, 800 F.2d at 902 (“Davis
did not determine at what point in the boarding process a pas-
senger may decide not to fly and thereby withdraw his
implied consent.”); Homburg, 546 F.2d at 1352 (“Davis does
not state specifically that the consent to additional searches
after a preliminary screening may be revoked if a passenger
agrees not to board the plane.”). Following Davis, however,
we have addressed this question a number of times.

                                   1.

  On the one hand, we have implied in a number of cases that
a prospective passenger may elect not to fly so as to avoid a
search at any time.5

   Thus, in United States v. Miner, 484 F.2d 1075, 1076 (9th
Cir. 1973), when the defendant attempted to check in for his
flight, one of the ticket agents determined that the defendant
fit the Federal Aviation Administration’s profile for airline
highjackers. Accordingly, airline employees escorted the
defendant to “a different area of the airport” that was “segre-
gated from the normal boarding area,” and asked him to walk
through a magnetometer. Id. at 1076-77. The defendant
agreed. Id. at 1076. Although the magnetometer alarm was
  5
    Of course, even under these cases, a prospective passenger who
revokes his consent may be lawfully subjected to a Terry stop-and-frisk
or, if supported by probable cause, a full search. E.g., Homburg, 546 F.2d
at 1352-54.
                    UNITED STATES v. AUKAI                 2849
not triggered, the airline employees nonetheless asked the
defendant to open a small suitcase that he was carrying. Id.
The defendant initially refused, but, after further requests,
eventually relented, at which point the airline employees
found amphetamine pills. Id. The district court denied the
defendant’s motion to suppress the evidence, and the defen-
dant was convicted of possessing amphetamine pills with
intent to distribute in violation of 21 U.S.C. § 841(a)(1). Id.

   We remanded so that the district court could conduct an
evidentiary hearing to determine whether the defendant’s ulti-
mate acquiescence to the airline employees’ repeated requests
to search his suitcase was in fact voluntary rather than the
product of duress. Id. at 1077. In so doing, we explained that
although the defendant’s “approaching the counter with the
obvious intention of boarding a plane amounted to an implied
‘consent’ within the meaning of Davis,” his initial refusal to
consent to the search of his suitcase “was an apparent with-
drawal of the implied ‘consent.’ ” Id. at 1076. Citing Davis,
we held: “At that point, the airline employees would have
been justified in refusing to permit him to fly, but they could
not compel him to submit to further search. Asking [him] to
open his suitcase could be justified only if he continued to
manifest an intention to board the plane, or if he otherwise
consented to the search.” Id. (internal citation omitted).

   Likewise, in United States v. Moore, 483 F.2d 1361, 1362
(9th Cir. 1973), the defendant attempted to check in for a
flight, but, in the opinion of a customs agent, could not satis-
factorily identify himself as the person to whom the ticket had
been issued. Accordingly, he was told he would not be per-
mitted to board the airplane, at which point the defendant
demanded the return of his two suitcases, which had already
been loaded onto the airplane. Id. at 1362-63. Upon retrieving
them, the defendant attempted to leave the terminal, but cus-
toms agents “drew him aside to an unoccupied boarding
area,” and searched a compartment within one of the suitcases
despite his refusal to permit them to do so. Id. at 1363. They
2850                 UNITED STATES v. AUKAI
discovered marijuana. Id. The district court denied the defen-
dant’s motion to suppress the evidence, and he was convicted
of possessing marijuana with the intent to distribute in viola-
tion of 21 U.S.C. § 841(a)(1). Id. at 1362. We reversed his
conviction, id. at 1364, holding in relevant part that the defen-
dant’s “bag was not searched as part of an administrative
screening search of airline passengers’ carry-on luggage such
as was approved in [Davis],” in part because he “clearly indi-
cated his desire to relinquish the opportunity to board the
flight before the search was made.” Id. at 1363.

   In United States v. Homburg, 546 F.2d 1350, 1351 (9th Cir.
1976), just before the defendant’s “carry-on suitcase was sub-
jected to x-ray inspection and he went through the magnetom-
eter” at a security checkpoint, airport officials were notified
of a bomb threat. As the defendant passed through the check-
point, security officials noticed a rectangular bulge in the
front portion of the defendant’s pants. Id. After passing
through the checkpoint, the defendant went to a restroom and
was followed by a security officer. Id. The defendant “went
inside a toilet stall and the officer heard a ‘cracking or rustling
sound, like a plastic bag or something of that nature’ coming
from inside the toilet stall.” Id. (internal citation omitted).
Then, after about fifteen minutes, the defendant exited the
stall. Id. “[T]he bulge in his trousers was gone and he was car-
rying his suitcase normally. [The defendant] then took his
place in the boarding line, nervously watching security offi-
cers.” Id. A security officer approached the defendant and told
him that he would have to be “reinspected.” Id. The defendant
initially complied, but, upon returning to the security check-
point, stated that he wished to leave the boarding area. Id. He
was then forcibly detained, and the security officers opened
the suitcase, finding heroin and cocaine within. Id. The defen-
dant was charged with possession of heroin with the intent to
distribute in violation of 21 U.S.C. § 841(a)(1) and possession
of cocaine in violation of 21 U.S.C. § 844, and moved to sup-
press the evidence. Id. at 1351-52. The district court denied
the motion, and the defendant was convicted. Id.
                    UNITED STATES v. AUKAI                   2851
   On appeal, we affirmed on the grounds that the search was
justified as a Terry stop-and-frisk. Id. at 1352-54. However,
before doing so, we expressly considered and rejected the
notion that the defendant had consented to the search or other-
wise relinquished Fourth Amendment protections merely by
passing through the security checkpoint and entering the
secured boarding area:

       The government argues that the search of [the
    defendant] took place in what it terms a “critical
    zone” which it compares to a border crossing and
    where, it argues, “special Fourth Amendment con-
    siderations apply.” The government submits that
    “once a passenger enters a secured boarding area, he
    relinquishes any right to leave without being
    searched if a security officer’s suspicions are
    aroused.” The cases the government cites come pri-
    marily from the Fifth Circuit which does appear to
    have adopted a view of airports as similar to border
    crossings and qualitatively different from the home
    or the street for Fourth Amendment purposes.

       While there is authority from this circuit to sup-
    port the government’s view of airports generally [cit-
    ing United States v. Doran, 482 F.2d 929, 931 n.1
    (9th Cir. 1973)], we cannot accept the government’s
    argument that a passenger in a secured boarding
    area may not, as a general proposition, leave the
    area rather than submit to additional searches. Such
    a view runs contrary to the rationale of United States
    v. Davis, 482 F.2d 893 (9th Cir. 1973). In that case,
    we held that the justification for warrantless screen-
    ing searches is the implied consent of the passenger.
    “[A]s a matter of constitutional law,” we stated in
    Davis, “a prospective passenger has a choice: he
    may submit to a search of his person and immediate
    possessions as a condition to boarding; or he may
    turn around and leave.” 482 F.2d at 913. Davis does
2852                UNITED STATES v. AUKAI
    not state specifically that the consent to additional
    searches after a preliminary screening may be
    revoked if a passenger agrees not to board the plane.

Id. at 1352 (emphasis added and citations omitted). In Hom-
burg, we noted:

    Davis strongly indicates . . . that a party may revoke
    his consent to be searched any time prior to boarding
    the plane, even when he has passed beyond the ini-
    tial screening point, if he agrees to leave the board-
    ing area. Other decisions of this court have also
    recognized that a passenger always maintains the
    option of leaving. See, e.g., United States v. Miner,
    484 F.2d 1075 (9th Cir. 1973); United States v.
    Moore, 483 F.2d 1361 (9th Cir. 1973). We must
    therefore reject the government’s view of its power
    to search within the boarding area as too sweeping.
    Since the undisputed evidence indicates that appel-
    lant wished to leave the boarding area, the trial judge
    erred in finding the search reasonable under the gen-
    eral doctrine of implied consent.

Id. at 1352. Nevertheless, we are not bound by this passage
because it is dicta. Indeed, the issue of implied consent to a
secondary search was irrelevant in Homburg because there,
authorities had reasonable suspicion to conduct a Terry stop-
and-frisk. Moreover, our more recent decisions have undercut
the reasoning of the quoted passage. See infra Section III.A.2.

   Finally, in United States v. Henry, 615 F.2d 1223, 1225
(9th Cir. 1980), the defendant’s conduct while checking in at
the ticket counter aroused the ticket agent’s suspicion. So,
rather than allowing the defendant to check his briefcase at
the ticket counter, the agent told the defendant that he would
have to check his briefcase at the gate and, thus, pass his
briefcase through screening at the security checkpoint. Id.
There, the security officers ran the defendant’s briefcase
                     UNITED STATES v. AUKAI                  2853
through the x-ray machine twice and saw some “dark
objects.” Id. When the security officers asked the defendant
to open his briefcase, he refused and was told that he would
have to take the briefcase back to the ticket counter and check
it as baggage. Id.

   The defendant returned to the ticket counter, but the agent
took the briefcase and told the defendant to meet him back at
the security checkpoint. Id. at 1225-26. By the time the ticket
agent and his supervisor arrived at the security checkpoint, the
defendant had already gone to the boarding area. Id. at 1226.
The ticket agent and his supervisor left the briefcase at the
security checkpoint and proceeded to the boarding area,
where the supervisor told the defendant that unless he opened
the briefcase he could not take it with him. Id. “At this point
[the defendant] said, ‘I’ve got to have that bag in Dallas.
Okay.’ [The defendant] then turned away and boarded the
plane.” Id. Airline personnel then passed the briefcase through
the x-ray machine again, at which point a security agent said
she thought there might be a gun inside, and eventually forci-
bly opened the briefcase and discovered, among other things,
a loaded revolver. Id. The defendant was charged with know-
ingly delivering a briefcase in which there was a firearm to a
common carrier for shipment in interstate commerce without
giving written notice in violation of 18 U.S.C. §§ 922(e),
924(a), id. at 1225, and moved to suppress the evidence, id.
at 1227. The district court denied the motion, and the defen-
dant was convicted. Id.

    We affirmed the conviction, first concluding that the defen-
dant had impliedly consented to the x-ray scans that took
place before he boarded the airplane because “he was free to
take the briefcase and leave the airport altogether or to board
without taking or checking the briefcase, rather than submit
it to the x-ray scan.” Id. at 1229. As for the later search, which
we characterized as “not [having been] conducted as part of
the program of screening passengers attempting to board,” id.,
we concluded that the defendant had consented when, after
2854                   UNITED STATES v. AUKAI
being told that his briefcase would not be allowed on the
plane until it was searched, he said that he had to have the
briefcase at his destination and then boarded the plane, id. at
1230-31. In so doing, we implicitly held that the defendant’s
implied consent to the initial search did not compel him to
submit to all future searches. To the contrary, citing Davis, we
explained that the defendant’s consent to the search that took
place after he boarded was valid only to the extent it could
have been withdrawn. Id. Hence, although the defendant
never elected not to fly so as to avoid the later search, his abil-
ity to do so even after he passed through the security check-
point was never in doubt, and was the basis of a finding that
his consent to the later search was freely given.6

                                   2.

   Despite these cases and the rather sweeping language in
Homburg that “Davis strongly indicates . . . that a party may
revoke his consent to be searched any time prior to boarding
the plane . . . if he agrees to leave the boarding area” and “that
a passenger always maintains the option of leaving,” Hom-
burg, 546 F.2d at 1252, we nonetheless have held that under
certain circumstances a prospective passenger may not revoke
his consent even by electing not to fly.

   In United States v. Pulido-Baquerizo, 800 F.2d 899, 900
(9th Cir. 1986), the defendant approached the security check-
point and placed two briefcases onto the x-ray machine’s con-
veyor belt. The security officer operating the x-ray machine
noticed an object within one of the briefcases that he thought
might be a bomb, but neither he nor the other security officers
  6
   We note that Miner, Moore, Homburg and Henry were all decided
before September 11, 2001. However, we need not and therefore do not
decide whether the events of September 11, 2001, render those cases
anachronistic and, thus, whether the government’s interest in protecting
against terrorism by means of commercial airliners has so increased since
we decided these cases that we would now hold the searches there reason-
able.
                    UNITED STATES v. AUKAI                 2855
could conclusively identify it as such. Id. They ran the brief-
case through the x-ray machine a second time, but still could
not identify the object. Id. at 900-01. The officers then con-
ducted a secondary hand search of the briefcase, which dis-
closed a large quantity of cocaine. Id. Prior to trial, the
defendant moved to suppress the evidence obtained by the
search and statements he made thereafter, and the district
court granted the motion. Id. at 901.

   We reversed. Id. at 900. In what was the first case to
address the question of when a passenger may revoke his con-
sent by electing not to fly since Homburg and Henry, we
explained that “[w]hile Davis implies a passenger may with-
hold . . . consent [to secondary screening following an ‘incon-
clusive’ x-ray scan] by electing not to fly, Davis did not
determine at what point in the boarding process a passenger
may decide not to fly and thereby withdraw his implied con-
sent” and, thus, “Davis does not specifically hold that consent
to an additional search could be withdrawn after an inconclu-
sive x-ray scan if the passenger agreed not to board the
plane.” Id. at 902. We noted further that although “we refused
to adopt [in Homburg] a general doctrine of implied consent
in the context of airport luggage searches,” we nevertheless
“noted [in Henry] that the precise issue of whether implied
consent to a subsequent search existed by the mere fact of
placing luggage on the x-ray machine remained undecided.”
Id.

  [3] Having set forth our understanding of our prior prece-
dent, we then specifically rejected the defendant’s reliance on
Davis in arguing that he had made statements prior to the sec-
ondary search that “show[ed] he preferred to leave [the air-
port] rather than submit to the [secondary] search,” id. at 902,
and held:

    [T]hose passengers placing luggage on an x-ray
    machine’s conveyor belt for airplane travel at a
    secured boarding area impliedly consent to a [sec-
2856                UNITED STATES v. AUKAI
    ondary] visual inspection and limited hand search of
    their luggage if the x-ray scan is inconclusive in
    determining whether the luggage contains weapons
    or other dangerous objects.

Id. at 901. Accordingly, “[t]he requirement in Davis of allow-
ing passengers to avoid the search by electing not to fly does
not extend to a passenger who has already submitted his lug-
gage for an x-ray scan” where the initial screening is “incon-
clusive,” and, “[t]hus, if a potential passenger [wishes] to
avoid a [secondary] search [in the event of an ‘inconclusive’
initial screening], he must elect not to fly before placing his
baggage on the x-ray machine’s conveyor belt.” Id. at 902.

   We note that Pulido-Baquerizo is not in direct conflict with
earlier cases such as Miner and Homburg, which stand for the
principle that prospective passengers can have the power to
limit their consent to airport searches even after voluntarily
submitting to initial screening procedures. The existence and
scope of implied consent must be examined in light of all the
circumstances, and such circumstances—and correlated soci-
etal expectations—may change over time. See Davis, 482
F.2d at 913 (noting that the burden on the defendant must be
measured against “the clear necessities of current circum-
stances”); Miner, 484 F.2d at 1076 (examining whether
implied consent existed in light of societal and individual con-
tingencies, including that “concern over the problem of air-
plane hijacking was at its peak”). Earlier cases did not arise
in the context of now-familiar modern screening procedures,
in which the parallel use of magnetometer and x-ray scans is
practically ubiquitous, nor in the context of modern under-
standings about the class of objects that might present sub-
stantial danger on an airplane. See infra Section III.B.2. Our
holding in Pulido-Baquerizo with respect to the scope and
irrevocability of implied consent is consistent with the earlier
opinions in light of the changed circumstances, expectations,
and technology involved in modern air travel and airport
screening. See Pulido-Baquerizo, 800 F.2d at 901-02 (exam-
                      UNITED STATES v. AUKAI                     2857
ining what “free society is willing to tolerate” in light of con-
temporary circumstances).

   Recently, in Torbet v. United Airlines, Inc., 298 F.3d 1087
(9th Cir. 2002), we revisited our holding in Pulido-Baquerizo.
Torbet walked through the magnetometer at a security check-
point, and his carry-on bag passed through the x-ray machine,
all apparently without triggering an alarm or otherwise arous-
ing suspicion. Id. at 1088. Nevertheless, acting pursuant to a
policy of randomly searching bags, even without the slightest
suspicion that a particular bag contained weapons or explo-
sives, airport security personnel selected Torbet’s bag for
such a random search. Id. He refused to consent to the sec-
ondary search of his bag, stating instead that he wished sim-
ply to leave the airport. Id. Torbet was nevertheless detained,
and his bag was searched.7 Id. The search revealed nothing of
note. Id. Pursuant to 42 U.S.C. § 1983, Torbet then sued the
airline, airport, and police officer that conducted the search,
alleging in relevant part that the random search to which he
had not consented violated his Fourth Amendment right
against unreasonable searches insofar as the initial screening
did not arouse suspicion that his bag contained weapons or
explosives. Id. at 1088-89. The defendants moved for judg-
ment on the pleadings, which the district court granted. Id.

  [4] We affirmed and held that a potential passenger irrevo-
cably consents to a secondary screening when he voluntarily
submits to an initial screening that is “inconclusive” as to the
presence of weapons or explosives. Id. at 1089. We then inter-
preted the term “inconclusive” broadly:

      [A]n x-ray scan may be deemed inconclusive, justi-
      fying further search, even when it doesn’t affirma-
      tively reveal anything suspicious. “[F]irearms and
      explosives can be small and easily concealed.” Con-
  7
   Torbet’s person was not subjected to a secondary search. See Torbet,
298 F.3d at 1088.
2858                    UNITED STATES v. AUKAI
     sequently, any x-ray scan that doesn’t rule out every
     possibility of dangerous contents is, of necessity,
     inconclusive.

Id. at 1089-90 (emphases added) (internal citation omitted).8
Therefore, even when a secondary screening is triggered
solely as part of a systemized random search policy—the ini-
tial screening “doesn’t affirmatively reveal anything
suspicious”—the initial screening prohibits the potential pas-
senger from revoking his implied consent for the secondary
screening if there still is a chance the passenger may be carry-
ing as-yet-undetected weapons or explosives.9 In other words,
the “inconclusive” nature of a proper initial screening, by
itself, establishes that the potential passenger has impliedly
consented to a secondary screening.10
   8
     In Torbet, we disagreed with the district court’s interpretation of
Pulido-Baquerizo “that consent to an x-ray scan [itself] implies consent to
further search, regardless of whether the x-ray scan is ‘inconclusive’ or
‘flatly devoid of suspicious features.’ ” Torbet, 298 F.3d at 1089. Rather,
given that current airport screening cannot rule out every possibility of
weapons or explosives, we clarified Pulido-Baquerizo to hold instead that
“an x-ray scan may be deemed inconclusive, justifying further search,
even when it doesn’t affirmatively reveal anything suspicious.” Id.
Because the currently accepted class of dangerous items is far broader
than what current screening technology could conclusively rule out, the
district court’s interpretation of Pulido-Baquerizo in Torbet and our inter-
pretation of Pulido-Baquerizo currently have the same practical effect—
once a potential passenger voluntarily submits to an initial screening at an
airport, he or she cannot revoke consent to a secondary search.
   9
     We considered again the reasonableness of a random search during the
screening process at an airport security checkpoint in Marquez. 410 F.3d
at 616-18. However, we expressly did not consider whether the defendant
there elected not to fly so as to avoid the search, explaining that “[t]here
is no evidence before us that [he] ever changed his mind about flying to
Anchorage and that issue was neither briefed nor argued by the parties.”
Id. at 618.
   10
      Of course, a potential passenger does not impliedly consent to any and
all types of secondary search by submitting to an inconclusive initial
search. The scope of a potential passenger’s implied consent is circum-
                        UNITED STATES v. AUKAI                        2859
                                    B.

   [5] Having now surveyed our relevant precedent, we con-
clude that the secondary screening at issue here is most akin
to that which we held reasonable in Torbet. Both here and in
Torbet, the contested search occurred at the security check-
point, but after the prospective passenger had voluntarily
passed through initial screening, which, although it did not
“affirmatively reveal anything suspicious,” was nonetheless
“inconclusive” insofar as it did not “rule out every possibility
of dangerous contents.” Torbet, 298 F.3d at 1089-90. Accord-
ingly, we follow the reasoning underlying Torbet in holding
that Aukai impliedly consented to a secondary search of his
person by walking through the magnetometer, and that he
could not subsequently revoke his consent to the secondary
screening. We recognize, of course, that the screening here
was different from that in Torbet in three respects: (1)
whereas the initial screening here was conducted by a magne-
tometer, the initial screening in Torbet was conducted by an
x-ray machine; (2) whereas the contested search here was of
Aukai himself, the contested search in Torbet was of the pro-
spective passenger’s carry-on baggage rather than his person;
and (3) whereas the contested search here was triggered by
Aukai’s failure to present identification when checking in, the
contested search in Torbet was the product of random selec-
tion. Nonetheless, for the reasons explained below, we find
none of these differences of distinguishing significance.

scribed by the Davis test’s two other necessary elements, neither of which
are at issue in this case: “that [the secondary search] is no more extensive
nor intensive than necessary, in light of current technology, to detect the
presence of weapons or explosives, [and] that it is confined in good faith
to that purpose.” 482 F.2d at 913. Unlike the criminal search context
where a court infers the scope of implied consent from the particular
details surrounding an individual’s exchange with an officer, see Florida
v. Jimeno, 500 U.S. 248, 251 (1991), the Davis test systematizes the
inquiry according to society’s privacy expectations in light of airport
searches’ broad regulatory policy of preventing terrorism, see Pulido-
Baquerizo, 800 F.2d at 901-02.
2860                UNITED STATES v. AUKAI
                              1.

   [6] As explained above, in Torbet, we defined “inconclu-
sive” to encompass an x-ray scan that does not “affirmatively
reveal anything suspicious” insofar as it also does not “rule
out every possibility of dangerous contents.” Id. at 1089-90.
Thus, in Torbet, we upheld a secondary search resulting from
random selection, which, by definition, results in “searching
bags even without suspicion that a particular bag contained
weapons or explosives.” Id. at 1088. Nothing about this defi-
nition of “inconclusive” is necessarily limited to x-ray scans
as opposed to magnetometers. Rather, recognizing the limits
of current technology, see Davis, 482 F.2d at 913, we simply
acknowledged the fact that just because an x-ray machine
does not reveal weapons or explosives in a passenger’s carry-
on baggage does not mean that they are not there. Torbet, 298
F.3d at 1089-90; accord Pulido-Baquerizo, 800 F.2d at 901.
We find no reason to consider Aukai’s magnetometer search
any more conclusive than the x-ray scan at issue in Torbet. In
the first place, a magnetometer may allow small amounts of
metal through without alarming, either because the metal was
not detected or because the amount detected was below the
threshold at which the magnetometer alarms. Cf. Marquez,
410 F.3d at 617 (noting that a walkthrough magnetometer was
“less sensitive” than a handheld one); Doran, 482 F.2d at 930
(noting that a magnetometer was calibrated not to alarm for
small quantities of metal). Indeed, in the present case, the
metal objects that were (as it happens) in Aukai’s pockets did
not set off the walkthrough magnetometer’s alarm. More
important, it is hard to imagine how a magnetometer could
possibly detect prohibited items that do not contain metal. See
Permitted and Prohibited Items List, available at http://
www.tsa.gov/public/interapp/editorial/editorial_1012.xml
(listing among the prohibited items, for example, flammable
liquids, matches, and realistic replicas of certain prohibited
items). We therefore hold that, for the purposes of the implied
consent inquiry, the screening by the walkthrough magnetom-
eter did not “rule out every possibility of dangerous contents”
                    UNITED STATES v. AUKAI                2861
and was therefore “inconclusive” under Torbet, 298 F.3d at
1089-90.

                              2.

   We similarly find that, under the rationale of our prior
opinions, Aukai’s arguments are not saved simply because it
was his person, rather than his baggage, that was subjected to
a secondary search. We recognize, of course, that a search of
a prospective passenger’s person may implicate greater pri-
vacy concerns than does a search of his carry-on baggage and,
thus, that there may be instances where particularly intrusive
searches of a prospective passenger’s person cannot be per-
mitted even following “inconclusive” initial screening absent
consent, some particularized suspicion sufficient to justify a
Terry stop-and-frisk, or probable cause. However, like the
search in Pulido-Baquerizo, we believe that the magnetometer
scan and the subsequent search conducted here “involve[d]
only a slight privacy intrusion” that “we believe free society
is willing to tolerate,” because the “governmental interest in
detecting the weapons employed in airline terrorism is great”
and because the search was limited in scope to “the detection
of weapons, explosives, or any other dangerous devices and
[was] conducted in a manner which produces negligible social
stigma.” 800 F.2d at 901-02; see also Torbet, 298 F.3d at
1089-90.

   [7] There is no doubt that Aukai was on notice that his per-
son could be searched. See Pulido-Baquerizo, 800 F.2d at 902
(requiring notice). Furthermore, the government interest is
just as great here as in the cases involving baggage searches.
Indeed, the events of September 11, 2001, have highlighted
that items a passenger could carry in his pocket may be just
as dangerous as what his carry-on baggage could contain. See,
e.g., National Commission on Terrorist Attacks Upon the
United States, The 9/11 Commission Report: Executive Sum-
mary (2004), available at 2004 WL 1846272, at *2 (noting
that terrorists “turned [four planes] into deadly guided mis-
2862                UNITED STATES v. AUKAI
siles” using only “small knives, box cutters, and cans of Mace
or pepper spray”); see also Permitted and Prohibited Items
List, available at http://www.tsa.gov/public/interapp/editorial/
editorial_1012.xml (listing numerous prohibited items that are
pocket-sized). Moreover, the search itself involved “only a
slight privacy intrusion.” Pulido-Baquerizo, 800 F.2d at 901-
02. The security agents here used a wand to detect any metal
objects on Aukai’s person, patted the outside of Aukai’s pants
pockets, and directed Aukai to empty his pockets—all meth-
ods that were minimally intrusive to Aukai’s privacy in light
of his repeated non-cooperation. See Marquez, 410 F.3d at
616 (holding that a handheld magnetometer scan of a prospec-
tive passenger’s person was constitutionally permissible).
Finally, allowing a passenger in Aukai’s position to revoke
his consent prior to the secondary screening would, to the
same extent contemplated in Pulido-Baquerizo, “encourage
airline terrorism by providing a secure exit where detection
was threatened,” 800 F.2d at 902, and thus undermine the
essential deterrent purpose of such airport screenings. See
Davis, 482 F.2d at 908; Marquez, 410 F.3d at 617; see also
Torbet, 298 F.3d at 1090 (“[T]he Fourth Amendment does not
require that passengers be given a safe exit once detection is
threatened.”); Pulido-Baquerizo, 800 F.2d at 902 (noting that
an “airport screening agent has a duty to ferret out firearms
and explosive devices carried by passengers,” a duty that
“could not be fulfilled if the agent was prohibited from con-
ducting a visual inspection and limited hand search after an
inconclusive x-ray scan”). In light of these concerns, the fact
that Aukai’s person was searched, rather than his baggage,
provides no basis for distinguishing the rule enunciated in
Pulido-Baquerizo and Torbet—namely, that implied consent
to an inconclusive initial search cannot be revoked prior to a
secondary search at a contemporary airport screening station.

                               3.

  There is, of course, no question that our holding in Torbet
was in the context of a secondary screening that was the prod-
                    UNITED STATES v. AUKAI                 2863
uct of random selection. Nevertheless, we do not find random
selection to be materially distinct from the trigger for second-
ary screening here—that is, Aukai’s failure to present identifi-
cation upon checking in. Both depend on wholly objective
mechanisms for requiring secondary screening as opposed to
merely subjective evaluations by airline or security personnel.
By virtue of the objective criteria upon which they rely, both
suggest of themselves “the absence of any indicia of improper
motive.” Marquez, 410 F.3d at 618. Indeed, as with the ran-
dom selection upheld in Torbet, we have expressly upheld the
constitutionality of subjecting airline passengers who lack
identification to a more thorough search. See Gilmore v. Gon-
zales, 435 F.3d 1125 (9th Cir. 2006). Hence, we need not and
therefore do not decide today whether a secondary screening
triggered by nothing more than the subjective evaluation of
the prospective passenger by airline or security personnel vio-
lates the Davis test’s requirement that an airport search be
“confined in good faith to [detect the presence of weapons or
explosives],” see 482 F.2d at 913, rather than more objective
criteria such as a screening machine alarm being triggered
(Doran), a screening machine otherwise signaling the possible
presence of weapons, explosives or other destructive devices
(Pulido-Baquerizo), random selection (Torbet), or, as here,
the prospective passenger’s failure to present identification
upon checking in.

  AFFIRMED.
