                        RECOMMENDED FOR FULL-TEXT PUBLICATION
                            Pursuant to Sixth Circuit I.O.P. 32.1(b)
                                   File Name: 17a0118p.06

                 UNITED STATES COURT OF APPEALS
                               FOR THE SIXTH CIRCUIT



 UNITED STATES OF AMERICA,                             ┐
                                 Plaintiff-Appellee,   │
                                                       │
                                                       >      No. 16-6149
       v.                                              │
                                                       │
                                                       │
 MONTAI RILEY,                                         │
                              Defendant-Appellant.     │
                                                       ┘

                       Appeal from the United States District Court
                   for the Western District of Tennessee at Memphis.
                 No. 2:15-cr-20242-1—Sheryl H. Lipman, District Judge.

                                 Argued: March 16, 2017

                             Decided and Filed: June 5, 2017

                     Before: BOGGS, ROGERS, and COOK, Circuit Judges.

                                   _________________

                                       COUNSEL

ARGUED: Claiborne H. Ferguson, THE CLAIBORNE FERGUSON LAW FIRM, P.A.,
Memphis, Tennessee, for Appellant. Ashley C. Brown, UNITED STATES ATTORNEY’S
OFFICE, Memphis, Tennessee, for Appellee. ON BRIEF: Claiborne H. Ferguson, THE
CLAIBORNE FERGUSON LAW FIRM, P.A., Memphis, Tennessee, for Appellant. Marques T.
Young, UNITED STATES ATTORNEY’S OFFICE, Memphis, Tennessee, for Appellee.

       The court delivered a PER CURIAM opinion. BOGGS, J. (pp. 10–17), delivered a
separate concurring opinion.
 No. 16-6149                           United States v. Riley                            Page 2


                                      _________________

                                           OPINION
                                      _________________

         PER CURIAM. This case calls upon us to clarify the rules by which police may seek to
find miscreants: When a fugitive subject to an arrest warrant for armed robbery hides in a motel,
may the government track his cell phone’s GPS coordinates to locate and arrest him?

         Yes, the district court held—and we affirm, holding that the government’s detection of
Montai Riley’s whereabouts in this case, which included tracking Riley’s real-time GPS location
data for approximately seven hours preceding his arrest, did not amount to a Fourth Amendment
search under our precedent in United States v. Skinner, 690 F.3d 772, 781 (6th Cir. 2012). The
government used Riley’s GPS location data to learn that Riley was hiding out at the Airport Inn
in Memphis, Tennessee—but only after inquiring of the front-desk clerk did the government
ascertain Riley’s specific room number in order to arrest him. The GPS tracking thus provided
no greater insight into Riley’s whereabouts than what Riley exposed to public view as he
traveled “along public thoroughfares,” id. at 774, to the hotel lobby. Therefore, under Skinner,
Riley has no reasonable expectation of privacy against such tracking, and the district court
properly denied Riley’s motion to suppress evidence found upon Riley’s arrest.

                                                I

         On June 23, 2015, a state court in Kent County, Michigan, issued an arrest warrant for
Riley, having found probable cause to believe that he had committed armed robbery of a local
Check ’n Go store on June 22. Riley had allegedly entered the store, pointed a gun at the clerk,
instructed her to open the safe, and fled on foot with a “money box and money bags.” On June
25, Riley purchased a cell phone serviced by AT&T. A member of Riley’s family gave this
phone’s telephone number to Riley’s girlfriend “so she could contact him while he was ‘on the
run.’”   Riley’s girlfriend in turn disclosed the number to Special Deputy Joel Bowman, a
member of the United States Marshal Service Grand Rapids Apprehension Team. On June 26,
Bowman applied for and received an order from the 17th Circuit Court of Kent County,
 No. 16-6149                                    United States v. Riley                                       Page 3


Michigan, compelling AT&T to produce telecommunications records of Riley’s cell phone under
federal electronic-surveillance laws. See 18 U.S.C. §§ 2703, 3123, 3124.

         The court order compelled disclosure of call metadata such as inbound and outbound
phone numbers and cell-site location (CSL) data, as well as real-time tracking1 or “pinging” of
the latitude and longitude coordinates of Riley’s phone. Specifically, the order required AT&T
to disclose the following, potentially for two months, until August 26, 2015:

         16. Precision location of mobile device (GPS Location) such that service provider
         shall initiate a signal to determine the location of the subject’s mobile device on
         the service provider’s network or with such other reference points as may be
         reasonable [sic] available and a [sic] such intervals and times as directed by State
         Task Force Investigators and Deputy Marshals of the United States Marshal
         Service.




         1
            Cell-phone location tracking refers to all methods of tracking a cell phone, including gathering cell-site
location information (commonly referred to as CSL or CSLI) and tracking satellite-based Global Positioning System
(GPS) data. CSL data are generated when a cell phone connects with a cell tower in order to make or receive a call;
a phone may connect to and disconnect from multiple towers during the course of a phone call if, for example, the
caller is in motion during the call. GPS data, on the other hand, do not come from a cell tower. Rather, GPS data
reveal the latitude and longitude coordinates of the cell phone, regardless of whether a call is in progress, as
identified by satellites orbiting the Earth that connect to the phone. A cell phone’s GPS location can be identified so
long as the phone has GPS functionality installed (as smartphones almost universally do), the phone is turned on,
and the GPS functionality is not disabled. Finally, “pinging” is a word that may refer in some contexts to a cell
phone’s connecting to a cell tower (e.g., “the phone pinged the tower”), and in other contexts to a service provider’s
act of proactively identifying the real-time location of the cell phone when the cell phone would not ordinarily
transmit its location on its own (e.g., “AT&T pinged the phone”).
          In line with the practice of other courts that have discussed cell-phone tracking, we use “pinging” only in
the latter sense: to ping a cell phone is to send a signal, so to speak, to identify where the phone is at any given
moment. While pinging may in some cases employ CSL information (for example, by triangulating the location of a
phone while a call is in progress by using data gathered from multiple cell towers), the pinging at issue in this case,
as in most recent cases, involves only real-time collection of GPS data.
 No. 16-6149                                   United States v. Riley                                         Page 4


         Within hours of the issuance of the surveillance order, U.S. Marshals received real-time
GPS data revealing that Riley’s phone was located at the Airport Inn in Memphis.2 Task-force
deputies in the Marshals’ Memphis office went to the motel, showed the front-desk clerk a
picture of Riley, and determined that Riley had checked in under the name “Rico Shawn
Lavender” and was in Room 314. The deputies went to Riley’s room and knocked. Riley
opened the door and immediately attempted to shut it, but the deputies entered the room and
arrested Riley at some time between 8:50 and 9:00 p.m. A Smith & Wesson .22-caliber pistol
was in plain view on the bed, and Riley was subsequently indicted on one count of being a felon
in possession of a firearm, in violation of 18 U.S.C. § 922(g)(1).

                                                           II

         Following his arrest in Memphis, Riley was extradited to Wyoming, Michigan, where, on
October 6, 2015, he was sentenced in state court to 7.5 to 25 years of imprisonment for armed
robbery, with an earliest release date of January 13, 2023, and a latest discharge date of July 13,
2040. He then returned to the United States District Court for the Western District of Tennessee
to answer his federal firearm-possession charge. Riley twice moved to compel the government
to disclose information on how the government located Riley so quickly, asserting that “[t]here
was no known legal way that Mr. Riley’s location could have been located absent the use of

         2
           AT&T provided the cell phone’s GPS coordinates at various times, the first twenty-two of which are
detailed below. No evidence of record indicates whether Riley’s phone automatically transmitted its GPS
coordinates to AT&T (and if so, whether on a continuous basis or otherwise) or whether AT&T affirmatively sent a
signal to Riley’s phone to cause it to send AT&T its GPS coordinates. When viewed on a map, the majority of these
coordinates are scattered within the perimeter of the Airport Inn, but with insufficient precision—even if the Airport
Inn were only one story tall—to reveal which room, if any, the phone was in at the time of each ping.
     Time        Latitude (° North)   Longitude (° West)           Time        Latitude (° North)   Longitude (° West)
  1:45:28 p m.       35.061626           90.014795              4:47:50 p m.       35.060328            90.01649
  2:01:37 p m.       35.061584           90.014859              5:03:39 p m.       35.060425           90.016597
  2:17:51 p m.       35.060446           90.016597              5:25:26 p m.       35.060489           90.016726
  2:33:41 p m.       35.060479           90.016683              5:41:30 p m.       35.060489           90.016511
  2:49:31 p m.       35.060511           90.016683              5:57:28 p m.       35.060178            90.01664
  3:05:24 p m.       35.061294           90.015288              6:14:04 p m.       35.060393            90.01679
  3:21:43 p m.       35.060393           90.016618              6:29:53 p m.       35.061755            90.01458
  3:41:40 p m.       35.060403           90.016661              6:47:14 p m.       35.060232           90.017627
  4:00:08 p m.       35.060414           90.016468              7:04:51 p m.       35.060543           90.016425
  4:16:04 p m.       35.060382           90.016618              7:30:40 p m.       35.060307           90.016747
  4:31:58 p m.        35.06035           90.016747              7:46:32 p m.       35.060403           90.016618
 No. 16-6149                                   United States v. Riley                                     Page 5


illegal cell tracking technology,” and that disclosure was required to allow Riley to bring a
constitutional challenge to whatever technology was used. The district court granted Riley’s
second motion to compel.

        Attaching copies of the state court’s surveillance order, Riley moved to suppress the
pistol found in his motel room as the fruit of an unconstitutional search, arguing that whatever
method the government had used to find him—whether by GPS pinging, a “cell-site simulator”
such as a “DirtBox, Stingray, etc.,” or otherwise, Mot. to Suppress, R. 35 at 3—intruded upon
Riley’s reasonable expectation of privacy and thus required a search warrant.3 The government
opposed the motion, including with its response a fourteen-page exhibit listing the GPS
coordinates of Riley’s cell phone on 454 occasions starting June 26, 2015, and ending June 30,
2015. The first twenty-two entries are listed above. Ante, at n.2. On average, AT&T logged
approximately one “ping” every thirteen minutes, although, of course, Riley was arrested on the
first day of the tracking.

        The district court denied the motion on two alternative bases: first, on the ground that our
decision in Skinner justified short-term GPS tracking without a warrant; second, on the ground
that the warrant that had been issued for Riley’s arrest justified obtaining real-time GPS
information about Riley’s location in order to effectuate his arrest. Riley pleaded guilty to being
a felon in possession of a firearm, reserving his right to appeal the denial of his motion to
suppress, and was sentenced to forty-one months of imprisonment to run concurrently with his
state sentence but with a delayed start date of February 13, 2022.

        The sole question before us is whether the district court erred in holding that the
government did not violate Riley’s Fourth Amendment rights by compelling AT&T to disclose,
and then by subsequently using, the real-time GPS location of Riley’s cell phone over the course




        3
          The parties agree that the state court’s surveillance order, despite being issued pursuant to federal
electronic-surveillance laws, was not a valid search warrant that would on its own justify tracking Riley’s location
data.
 No. 16-6149                                   United States v. Riley                                      Page 6


of approximately seven hours.4 Because the sort of short-term tracking conducted here falls
squarely within the logic of our precedent in Skinner, we affirm.

                                                        III

        The Fourth Amendment protects individuals against unreasonable searches and seizures
of their “persons, houses, papers, and effects.” Law-enforcement officers conduct a “search”
when they seek to obtain information in either of two ways: (1) by physically trespassing upon
an individual’s person, house, papers, or effects, see United States v. Jones, 565 U.S. 400, 406–
07 (2012) (holding GPS tracking of a vehicle for twenty-eight days was a search when agents
physically trespassed upon the vehicle to install the tracking device), or (2) by intruding upon an
individual’s reasonable expectation of privacy, see Katz v. United States, 389 U.S. 347, 360–62
(1967) (Harlan, J., concurring) (holding eavesdropping on a payphone conversation by means of
an electronic listening and recording device, when the payphone door was closed, was a search;
noting “reasonable expectations of privacy may be defeated by electronic as well as physical
invasion”). Riley does not argue that the government committed a physical trespass of any sort,
and we decline to consider whether pinging a cell phone may constitute an electronic trespass,5
so only the ‘reasonable expectation of privacy’ test is applicable here.

        Both the Supreme Court and our court have declined to recognize as reasonable a
criminal suspect’s expectation of privacy in his location while moving along public
thoroughfares. See United States v. Knotts, 460 U.S. 276, 279–80 (1983) (holding the placement
of a radio transmitter by narcotics officers in a container of chemicals to be purchased by a
suspected methamphetamine manufacturer was not a search when officers used the transmitter to


        4
          Riley also attempts to raise a statutory argument on appeal. As the district court recognized, the statutes
that Riley relies upon only provide mechanisms for authorizing access to certain cell-phone data and do not prohibit
the government from otherwise tracking an individual’s GPS location data. Thus, the statutes cannot provide Riley
with the remedy he seeks—suppression of the evidence against him.
        5
          At oral argument, Riley sought to advance an argument that the government, by initiating a signal to
Riley’s cell phone rather than merely gathering data that the cell phone emitted on its own, had committed an
electronic or digital trespass that was technologically distinguishable from the tracking in Skinner. This argument
was not raised in Riley’s brief on appeal, however, and thus it is not properly before us. Moreover, Skinner
expressly contemplated tracking “cell site information, GPS real-time location, and ‘ping’ data,” 690 F.3d at 776,
and there is nothing in the record before us to indicate that the tracking here is technologically distinct from the
tracking that occurred in Skinner.
 No. 16-6149                           United States v. Riley                             Page 7


track a vehicle while it carried the transmitter along public roads to a cabin, but when the
transmitter did not enter the cabin itself); United States v. Skinner, 690 F.3d 772, 774–75, 776
(6th Cir. 2012) (holding government use of real-time cell-phone GPS data to track a suspected
drug trafficker as he traveled for three days in a “motorhome that was driven on public roads”
was not a search).

       In Skinner, we held that location data emitted by a “voluntarily procured” cell phone
could not be subject to a reasonable expectation of privacy, even if the cell-phone user had no
reason to expect that the government would compel the service provider to disclose those data.
Id. at 779. There, because “the defendant’s movements could have been observed by any
member of the public,” ibid., we held that it could not possibly be a Fourth Amendment violation
for law-enforcement officers to monitor those movements by using cell-phone location data just
because such electronic monitoring was more efficient than relying on visual surveillance alone.

       The fact that the defendant’s movements in Skinner were visible from public vantage
points was an important factor in our reasonable-expectation-of-privacy analysis. Entering an
individual’s home to observe his movements, even if by technological device rather than
physically, would much more likely raise Fourth Amendment concerns in light of the common
law’s protection of the home against government intrusion. As William Pitt, Earl of Chatham,
reportedly proclaimed during a debate in Parliament in 1763: “The poorest man may in his
cottage bid defiance to all the forces of the Crown. It may be frail; its roof may shake; the wind
may blow through it; the storm may enter; the rain may enter; but the King of England cannot
enter—all his force dares not cross the threshold of the ruined tenement!”           The Oxford
Dictionary of Quotations (2d ed. 1953), 379, quoted in Miller v. United States, 357 U.S. 301, 307
(1958). The two-and-a-half intervening centuries have seen little jurisprudential erosion of this
tenacious reverence for the sanctity of the home.

       The Supreme Court has made very clear, for example, that “obtaining by sense-enhancing
technology any information regarding the interior of the home that could not otherwise have
been obtained without physical ‘intrusion into a constitutionally protected area’ constitutes a
search.” Kyllo v. United States, 533 U.S. 27, 35 (2001) (emphasis added) (citation omitted)
(quoting Silverman v. United States, 365 U.S. 505, 512 (1961)) (holding government use of
 No. 16-6149                            United States v. Riley                              Page 8


thermal-imaging devices to monitor the heat being produced inside a home as part of a strategy
to detect indoor marijuana growing was a search where the devices were unavailable to the
general public, even though the devices were used only from outside the home without effecting
a physical trespass); United States v. Karo, 468 U.S. 705, 708–09, 713–15 (1984) (holding
government monitoring of a tracking device placed in a shipment of chemicals taken home by a
suspected drug dealer was a search where the agents tracked the device to locate the chemicals,
on several occasions, within the defendant’s house and various other private residences;
distinguishing Karo from Knotts on the sole basis that unlike in Knotts, in which “the record did
not show that the beeper was monitored while the can containing it was inside the cabin,” the
government in Karo had “surreptitiously employ[ed] an electronic device to obtain information”
about the interior of “a private residence, a location not open to visual surveillance,” in a way
that was not feasible without the aid of the device) (emphasis added).

       Searches “inside a home without a warrant are presumptively unreasonable.” Karo,
468 U.S. at 715; see also Silverman, 365 U.S. at 511 (holding that the right to privacy at home is
“[a]t the very core” of what the Fourth Amendment seeks to protect).               And the Fourth
Amendment’s full complement of protections “also applies to hotel rooms.” United States v.
Allen, 106 F.3d 695, 698 (6th Cir. 1997) (citing Hoffa v. United States, 385 U.S. 293, 301
(1966)).

       But using seven hours of GPS location data to determine an individual’s location (or a
cell phone’s location), so long as the tracking does not reveal movements within the home (or
hotel room), does not cross the sacred threshold of the home, and thus cannot amount to a Fourth
Amendment search. After all, the tracking in Knotts revealed the location of the cabin to which
the criminal suspects had traveled—but the tracking in Knotts was not a search because it
revealed no information about the interior of the cabin itself. Likewise here, the tracking
revealed only that Riley had traveled to the Airport Inn, not which room (if any) the phone was
in at the time of the tracking. And the tracking in Karo, while a search to the extent that the
tracking device there was monitored within private residences, was not a search at other times,
such as when the tracking device was monitored in one of the defendant’s vehicles “on its
trip . . . to the immediate vicinity of” a private residence. 468 U.S. at 719 (emphasis added).
 No. 16-6149                             United States v. Riley                               Page 9


       Therefore, the government did not conduct a search under the Fourth Amendment when it
tracked the real-time GPS coordinates of Riley’s cell phone on the date of Riley’s arrest. Skinner
upheld tracking that spanned three days; here, approximately seven hours elapsed between the
first ping and the time of Riley’s arrest. That Riley was arrested in a motel is of no moment, for
the government learned no more about Riley’s whereabouts from tracking his cell-phone GPS
data than what Riley exposed to public view by traveling to the motel lobby “along public
thoroughfares,” Skinner, 690 F.3d at 774—even if Riley meant to keep his location a secret, one
cannot expect privacy in one’s public movements.            And had Riley truly wished to avoid
detection, he could have chosen not to carry a cell phone at all, or to turn it off. The district court
thus correctly denied Riley’s motion to suppress.

       AFFIRMED.
 No. 16-6149                            United States v. Riley                             Page 10


                                       _________________

                                       CONCURRENCE
                                       _________________

       BOGGS, Circuit Judge, concurring.

                                                 I

       I write separately to highlight certain additional factors at play in this case that provide
additional comfort that our holding today is correct.

       At oral argument, the government conceded that if the GPS tracking had been precise
enough to identify a specific home or motel room in which Riley was hiding—rather than a
motel generally—Kyllo and Karo may have presented greater concerns:

               I think that, if these coordinates had been sufficient to identify a home or a
       hotel room, this could be a different case, but I think the fact here that the
       coordinates only get the police officers to the hotel lobby, essentially, and they
       then have to do additional work in terms of figuring out exactly what hotel room
       he’s in, makes this case different from if he had been identified in his home, and
       makes this case more akin to Skinner.

Tr. of Oral Arg. 20:06-20:35.

       But our precedent in Skinner governs because the tracking here brought the law-
enforcement officers only as far as the lobby of the Airport Inn—a public area—and the officers
then had to ask the front-desk clerk to determine Riley’s whereabouts within the confines of a
specific hotel room.

       I would note that in cases like Riley’s, even tracking GPS data within a home or a hotel
room may fail to rise to the level of a Fourth Amendment search when the individual whose cell-
phone location is tracked is a fugitive subject to a valid arrest warrant, and when the law-
enforcement officers tracking him have at least reasonable suspicion that he is in possession of
the phone being tracked. Thus, for the reasons that follow, I would hold that Riley’s Fourth
Amendment claim fails, alternatively, because he was a fugitive subject to a valid arrest warrant,
and because the officers here had reasonable suspicion that he was in possession of the phone
that they were tracking.
 No. 16-6149                           United States v. Riley                           Page 11


                                 A. The Third-Party Doctrine

       Supplementing the general Fourth Amendment unreasonable-search framework based on
the Supreme Court’s rulings in Katz and Jones is the so-called third-party doctrine, according to
which one can have no reasonable expectation of privacy in information knowingly disclosed to
a third party, and thus no Fourth Amendment claim can lie for the acquisition and use by law-
enforcement agents of such information. See United States v. Miller, 425 U.S. 435, 441–43
(1976) (holding government-compelled disclosure of “a depositor’s private [bank] records” was
not a Fourth Amendment search because “the Fourth Amendment does not prohibit the obtaining
of information revealed to a third party and conveyed by him to Government authorities, even if
the information is revealed on the assumption that it will be used only for a limited purpose and
the confidence placed in the third party will not be betrayed”); Smith v. Maryland, 442 U.S. 735,
742 (1979) (holding government-compelled installation of a pen register to track phone numbers
dialed from a specified telephone-service subscriber’s landline phone was not a search where the
pen register was installed on the telephone company’s property and where the outbound phone
numbers were voluntarily disclosed to the telephone company and therefore could not reasonably
be considered private).

       But Kyllo, decided well after both Miller and Smith, expressly rejected the notion that the
government’s use of thermal-imaging devices to detect heat within the defendant’s home could
be justified on the ground that the defendant “exposed” his activity “to the public” by emitting
heat waves that could be detected from a public vantage point. Kyllo, 533 U.S. at 44 (Stevens, J.,
dissenting) (drawing analogies between heat waves that “enter the public domain if and when
they leave a building” and discarded garbage, California v. Greenwood, 486 U.S. 35, 45 (1988),
pen-register data, Smith, 442 U.S. at 742, and subpoenaed utility records). In short, the third-
party doctrine does not lay bare to Big Brother’s watchful eye every activity conducted within
the home just because someone outside the home might be able to detect its occurrence. The
third-party doctrine, therefore, would likely be insufficient on its own to support government-
compelled tracking of location data that revealed movements within a home or hotel room.
 No. 16-6149                               United States v. Riley                            Page 12


                               B. The Fugitive–Suspect Distinction

        A key distinction between this case and Kyllo, Karo, Knotts, and Skinner, which further
supports our holding, is that the government tracked Riley’s cell phone only after a valid warrant
for his arrest had already been issued, whereas the defendants in Kyllo, Karo, Knotts, and
Skinner were criminal suspects but not fugitives.           And although the text of the Fourth
Amendment does not itself imply that individuals on the run from arrest warrants have a
diminished expectation of privacy, the Supreme Court’s decision in Payton v. New York,
445 U.S. 573 (1980), as corroborated by significant historical evidence of the original meaning
of the Fourth Amendment, provides strong support for the proposition that they do. Id. at 592–
96, 603 (holding that where law-enforcement officers have a valid arrest warrant and reasonably
suspect that the individual subject to arrest is inside his home, they may enter the home and
arrest the individual without first obtaining a search warrant to do so).

        The logic in Payton is that the Fourth Amendment requires the government to obtain a
warrant before entering the arrestee’s home, but whether the warrant must be an arrest warrant or
a search warrant is not a question answered definitively by the constitutional text, and in the case
of a fugitive subject to a valid arrest warrant, the arrest warrant “will suffice to interpose the
magistrate’s determination of probable cause between the zealous officer and the citizen.” Id. at
602–03 (“If there is sufficient evidence of a citizen’s participation in a felony to persuade a
judicial officer that his arrest is justified, it is constitutionally reasonable to require him to open
his doors to the officers of the law.”).

        Surely, if the issuance of a valid arrest warrant may reasonably require an individual to
open the doors of his home, which stands at the “very core” of Fourth Amendment protection,
Silverman, 365 U.S. at 511, then it may reasonably require the same individual to open the doors
of his phone—at least so far as to disclose the longitude and latitude coordinates emitted by a
phone that the individual chooses to carry and turn on. Allowing law-enforcement agents to
track a fugitive’s cell-phone location data, including GPS location data within the home, thus
falls well within the logic of Payton without contravening Kyllo or Karo: so long as a valid arrest
warrant has been issued, law-enforcement officers who reasonably suspect that a cell phone is in
 No. 16-6149                            United States v. Riley                              Page 13


the possession of the subject of the warrant may track that cell phone’s location in order to
facilitate the execution of the warrant, without implicating the Fourth Amendment.

 C. Factors Weighing Against the Fugitive’s Expectation of Privacy in GPS Location Data

       Several considerations, none of which is independently sufficient, support the proposition
that a cell-phone service provider’s records of a fugitive’s cell-phone location data are not
private for Fourth Amendment purposes.

       First, the subject of the surveillance is a fugitive. While a fugitive does not forfeit all his
expectation of privacy—after all, under Payton, law-enforcement officers may not simply break
into a fugitive’s home to arrest him without at least some reason to believe that the fugitive is
inside—the most compelling factor in favor of allowing the government to track a fugitive’s cell
phone regardless of the phone’s location is that the fugitive is the subject of a valid arrest
warrant.

       In addition to the rule in Payton, which allows officers to enter an arrestee’s home to
effectuate the arrest with only reasonable suspicion that the arrestee is at home, the Supreme
Court has held that law-enforcement officers in “hot pursuit” of their quarry have a limited right
to enter private homes without a search warrant. See Warden v. Hayden, 387 U.S. 294, 298, 310
(1967) (holding exigent circumstances validated warrantless entry into a home to search for a
suspected armed robber who had reportedly entered less than five minutes earlier). There is
some historical support for holding that a fugitive’s expectation of privacy at home is diminished
as well: at common law, officers may have had at least some authority enter a home to execute
an arrest warrant after first making a demand. See Payton, 445 U.S. at 616 (citing Semayne’s
Case, 5 Co. Rep. 91a, 77 Eng. Rep. 194 (K. B.) (1603)) (“[I]n cases of felony, the officers were
required to announce their presence, demand admission, and be refused entry before they were
entitled to break doors.”); but see 3 William Blackstone, Commentaries *288 (“[F]or the most
part not so much as a common citation or summons, much less an arrest, can be executed upon a
man within his own walls.”). Arguably, one who refuses the lawful demand of the King to enter
and execute an arrest warrant is in an analogous position to one who is on the run from a lawful
 No. 16-6149                             United States v. Riley                             Page 14


arrest warrant, and so the two could reasonably be expected to have similar expectations of
privacy.

       Second, the information gathered in cases like Riley’s is location data, not call content.
To be sure, Kyllo and Karo set a fairly low threshold level of intrusion within the home at which
surveillance becomes a search. But tracking Riley’s cell-phone location provided no more
information about the interior of Riley’s home (or motel room) than did the tracking device in
Karo, and it provided far less information than did the thermal-imaging device in Kyllo. While
GPS tracking is “accurate within about 50 feet,” United States v. Carpenter, 819 F.3d 880, 889
(6th Cir. 2016), and is thus more precise than CSL data, which ballparks a cell phone’s location
within a “radial wedge extending between one-half mile and two miles in length” based on the
cell towers to which it connects, ibid., GPS coordinates reveal nothing other than the location of
the phone: no call content, no text-message or email content, and no application data.

       Third, the tracking in cases like Riley’s is limited in duration and reach. In Jones,
Justices Sotomayor and Alito wrote separate concurring opinions in which they commented that
“the use of longer term GPS monitoring in investigations of most offenses impinges on
expectations of privacy.” Jones, 565 U.S. at 430 (Alito, J., concurring in the judgment); id. at
412 (Sotomayor, J., concurring) (quoting id. at 430). Justice Alito’s comment, however, pertains
to investigations, not manhunts. And for fugitives subject to an arrest warrant, the duration of
surveillance, which will ordinarily be relatively short-term (i.e., commencing after the issuance
of an arrest warrant and ending when the fugitive is found), is less of a concern than for those
who are simply suspects of an investigation.

       Fourth, although I noted that the third-party doctrine itself does not provide a basis for
using technology to detect activity within a home, the fact that cell-phone users voluntarily
disclose their location data by keeping their phones turned on weighs against finding their
location data to be private. It is, of course, unclear whether Riley knowingly disclosed his
location data (the record does not indicate whether Riley was aware of the cell phone’s GPS
feature, nor does it include any terms of Riley’s cell-phone service contract that would reveal
whether Riley agreed to allow AT&T either to gather and store his GPS location data or to
initiate signals to Riley’s phone to facilitate real-time tracking, if AT&T in fact did that). But the
 No. 16-6149                             United States v. Riley                              Page 15


fact that Riley chose to carry a cell phone (as distinguished from the tracking devices carried
unwittingly by the defendants in Karo and Knotts) certainly weighs in favor of allowing the
government to access AT&T’s records of Riley’s cell-phone location in order to arrest him, even
if those records were generated only in response to requests from the government for real-time
location tracking. A criminal hiding from an arrest warrant “can hardly complain,” Skinner,
690 F.3d at 774, about the burden of having to evade detection without constant use of a cell
phone.

         To say otherwise would be to require the government to avert its eyes from GPS location
data that are freely available to the wireless providers that facilitate fugitives’ use of cell phones,
but the Fourth Amendment does not require such willful blindness. Cf. Ex parte Jackson,
96 U.S. 727, 737 (1877) (holding that the content of letters and sealed packages deposited in the
mail could be examined only upon the issuance of a warrant, but the content of printed matter
“left open for examination,” such as newspapers, and, by implication, the mailing information on
the outside of a sealed letter, was not protected by the Fourth Amendment).

         The logic in Jackson, in which a defendant was convicted of depositing “a circular
concerning a lottery offering prizes” into the United States mail in violation of a federal statute,
id. at 727–28, is that one using the mail—no matter how essential to daily life the mail might
have been in 1877—assumes the risk that the government will see, and will have no duty to avert
its eyes from, information left open to be seen. Under the logic of Jackson, one who voluntarily
but unknowingly left a letter unsealed and then mailed it would have no recourse in the event
that a government official found evidence of a crime in the letter and used it to secure a warrant.
Perhaps the current state of cell-phone location data is similar: as a general matter, cell-phone
users may not have any idea of the extent to which their cell phones are broadcasting their
location (whether in the form of CSL data or GPS location data). But in choosing to carry and
turn on and leave on cell phones equipped with GPS and other location-based services, people
arguably assume the risk that their cell-phone service providers may disclose to the government
the location data they acquire—at least in the absence of a contractual agreement between the
consumer and the service provider that would prohibit or restrict such disclosure. And while the
strong Fourth Amendment protections afforded to the home may yet protect some cell-phone
 No. 16-6149                              United States v. Riley                              Page 16


location data emitted from within the home from being tracked by the government, a fugitive
who carries a cell phone turned on must assume the risk that the government is able to track him
wherever he may be.

       Of course, law-enforcement officers could track down fugitives the old-fashioned way:
they could put out alerts to be posted upon grocery-store bulletin boards for oblivious shoppers
to disregard, and they could wait for the fugitives to be caught, perhaps, when they commit some
other crime from which they are less successful in flight.            But that cannot be what the
Constitution requires; when fugitives use sophisticated cell phones to evade detection, whether
by communicating electronically, finding hideouts, soliciting willing abettors, or perhaps
acquiring false documents and the like, it only makes sense that law-enforcement agents be able
to track fugitives’ cell-phone location data to execute valid arrest warrants.

       Accordingly, even setting aside the fact that the government’s GPS location tracking here
revealed only information about the public movements of Riley’s cell phone, Riley’s Fourth
Amendment claim fails because Riley was a fugitive from justice who lacked a reasonable
expectation of privacy in his whereabouts, and the district court was correct to deny Riley’s
motion to suppress.

                                                  II

       Unlike the traditional children’s game of hide-and-seek, which tolerates most means of
finding those who are hiding, the Fourth Amendment separates cop from robber by the
requirement that “a neutral and detached magistrate,” Johnson v. United States, 333 U.S. 10, 14
(1948), issue a warrant based on probable cause that the robber has committed the robbery.

       Once a valid warrant has issued, however, the game changes: the robber may not both
seek refuge from execution of the warrant and simultaneously broadcast his location by carrying
a GPS-enabled cell phone.

       GPS data, unlike CSL data, can locate a tracked object to within tens of feet of its actual
location. Still, as in this case, it may not be sufficiently precise to pinpoint the exact location of a
GPS-enabled cell phone. To the extent that GPS tracking reveals location information that
 No. 16-6149                            United States v. Riley                            Page 17


would otherwise be available from public vantage points, such as identifying Riley’s presence at
the Airport Inn in this case, our precedent in Skinner permits at least short-term tracking of such
location information.     Even within the confines of a home or a hotel room, the Fourth
Amendment does not shield a fugitive’s cell phone from being located while turned on: a cell-
phone service provider’s records of the phone’s location are not private, and their use by law
enforcement, compelled or otherwise, is not a search under the Fourth Amendment so long as the
officers have at least reasonable suspicion that the phone they are tracking is in the possession of
the fugitive they seek.

       Finally, I would note that our opinion today does not—because it needs not—address
many questions that will almost certainly arise in future geolocation cases, such as whether or
when the government may use GPS location data to track individuals other than fugitives within
the home. Nor does it address the questions that will surely arise as technology continues to
develop. Perhaps, for example, if government agents gain the ability to activate and monitor the
microphone, camera, or video recorder on an individual’s cell phone without the individual’s
knowledge, the greater degree of intrusion from such audiovisual monitoring could materially
affect even a fugitive’s expectation of privacy in the data transmitted from his cell phone. And
nothing in our opinion curtails the power of federal and state legislatures to craft legislation
against cell-phone location tracking if they wish. Indeed, our opinion today does not address
whether existing protections under the Stored Communications Act or elsewhere may already
impose additional requirements on government agents seeking to engage in the sort of GPS
location tracking that the Marshals used here to track Riley, because the only question before us
is whether the tracking violated Riley’s constitutional rights—and it did not.
