US Supreme Court weighs geofence searches and the third-party doctrine

In April, the U.S. Supreme Court heard oral arguments in Chatrie v. United States, a case that will define the rules for how the Fourth Amendment applies to police searches of consumers' historic digital location data--data that corporations collect and monetize through targeted advertising. Although it is impossible to predict exactly how the Court will rule, oral argument suggested skepticism among several justices toward the government's contention that the third-party doctrine means that whenever people permit companies to track their location history they necessarily surrender all Fourth Amendment protection for that data.

The government's argument, if accepted, would mean that police could obtain any user's historic location data--say from Google Maps, Apple Watches, Uber, X, or any other company's app that tracks location--without needing a search warrant. The government stated as much in its brief: "Although investigators prophylactically secured a warrant in this case, their receipt of short-term location information from Google was not actually a Fourth Amendment 'search' that might require one." Brief for the United States, No. 25-112, at 14. A number of the justices, however, appear to have reservations about handing police such wholesale power.

I. Geofences: a new Fourth Amendment problem

Chatrie involves a geofence warrant that police served on Google. A geofence search uses latitude and longitude coordinates to draw an imaginary boundary around a crime scene and requires a company to identify cell phones using its applications that were inside the area during a defined past time period. Chatrie arose from an armed robbery of a Virginia credit union. Lacking suspects, police obtained a geofence warrant directing Google to search its Location History database for devices within 150 meters of the bank during the hour before and after the robbery. Google returned anonymized identifiers for 19 phones, one of which investigators eventually linked to Okello Chatrie. Chatrie conditionally pleaded guilty while preserving his right to challenge the search.

There are two important aspects of geofence searches. First, geofence searches are only possible because modern smartphones allow precise location tracking and companies retain historical location data. The Fourth Amendment, enacted in 1791, provides no direct guidance for such technology.

Second, geofence searches differ from traditional searches. A traditional search has a known suspect and seeks further evidence to link that suspect to the crime. In contrast, a geofence search has a known crime but no suspects. Therefore, a geofence search retrospectively identifies everyone with a cell phone within the defined crime area during the relevant time window, in order to generate potential suspects. This novel technique could permit broad searches in hopes of identifying unknown suspects. Indeed, the 5th U.S. Circuit Court of Appeals has rejected geofence searches entirely, holding that "geofence warrants are general warrants categorically prohibited by the Fourth Amendment" and therefore are unconstitutional. United States v. Smith, 110 F.4th 817, 838 (5th Cir. 2024).

This new type of search has pushed existing Fourth Amendment doctrine into difficult doctrinal territory. The Supreme Court first recognized the qualitative differences posed by digital location searches in 2018, in Carpenter v. United States, in the context of cell-site location tracking. The Court emphasized that technology now allows retrospective tracking of people's movements that was previously impossible: "[T]he Government can now travel back in time to retrace a person's whereabouts.... [T]his newfound tracking capacity runs against everyone." Carpenter v. United States, 585 U.S. 296, 312 (2018) (holding that individuals retain a Fourth Amendment privacy interest in historic cell-site location information despite its disclosure to phone companies). But Carpenter involved tracking one known person's phone over time. A geofence search is a step further because it potentially sweeps in all people with cell phones within the fence.

Turning back to Chatrie, on appeal a divided panel of the 4th U.S. Circuit Court of Appeals applied the third-party doctrine and held that "Chatrie did not have a reasonable expectation of privacy in two hours' worth of Location History data voluntarily exposed to Google." The panel therefore concluded that the "government did not conduct a search when it obtained this information from Google." United States v. Chatrie, 107 F.4th 319, 325 (4th Cir. 2024), aff'd en banc per curiam, 136 F.4th 100 (4th Cir. 2025), cert. granted in part, Chatrie v. United States, __ U.S. __, 2026 WL 120676 (Jan. 16, 2026). The 4th Circuit then reheard the appeal en banc, but failed to produce a majority opinion, affirming the conviction in a one-sentence per curiam decision accompanied by multiple concurrences and a dissent.

II. The third-party doctrine confronts new technology

So, what is the third-party doctrine, which the Chatrie panel opinion relied upon to conclude that a geofence search is not a search at all? The idea is that if you knowingly give your information to someone else, then you also surrender any reasonable expectation of privacy in that information--so you cannot complain under the Fourth Amendment if that third party subsequently gives your information to the police, even if the third party promised you they would keep your information confidential. The doctrine was stated most broadly in United States v. Miller, where the Supreme Court held that police could obtain a depositor's bank records from a bank without needing a search warrant:

[T]he 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.

United States v. Miller, 425 U.S. 435, 443 (1976).

Miller's statement is broad--but it has never been completely true. For example, when you mail a letter you are voluntarily giving it to a third party, with the assumption that they will deliver it but will not open and read the contents. Miller notwithstanding, this does not mean that the police can open and read your letters without obtaining a search warrant. As long ago as 1877, the Supreme Court explicitly held that mailed letters can only be searched by a court-issued warrant: "Letters and sealed packages in the mail... can only be opened and examined under warrant." Ex parte Jackson, 96 U.S. 727, 733 (1877) (cleaned up).

More recently, in Carpenter, the Supreme Court rejected the government's argument that the third-party doctrine meant police could obtain historic cell phone location data from phone companies without a warrant. There, the police tracked a defendant's cell phone for 127 days, using the automatic location pings his phone sent to the company's cellular towers. Since location pings are inherent to using a cell phone, the government contended that--by voluntarily using a cell phone--the defendant had given his location information to the phone company and no longer had Fourth Amendment protection.

The Supreme Court disagreed. The level of location detail that cell phone tracking provides makes it categorically different, so that users do not give up their reasonable expectation of privacy, even though the phone company knows their location. "Given the unique nature of cell phone location records, the fact that the information is held by a third party does not by itself overcome the user's claim to Fourth Amendment protection.... We hold that an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through [cell-site location information]." Carpenter, 585 U.S. at 309-10. Thus, when police want the phone company to give them a suspect's cell phone location history, that is a Fourth Amendment search and the police need to apply to a judge for a search warrant.

III. Does opting in to location tracking matter?

But what is the difference between Chatrie and Carpenter that the government argues makes the third-party doctrine applicable to geofence searches? The answer is that Chatrie affirmatively opted in to Google's Location History, by enabling the feature after viewing a warning that doing so would allow Google to track his movements. To the 4th Circuit panel majority, that affirmative conduct made all the difference, since not all of Google's users allow Location Tracking. Only "one-third of active Google users have enabled Location History." Chatrie, 107 F.4th at 323. In contrast, while the defendant in Carpenter voluntarily used a cell phone, he did not specifically turn on cell-site tracking, since that is automatic to all cell phones.

That is a potentially legitimate distinction. Under classic third-party doctrine, the extent to which a person exposes his information knowingly and voluntarily to a third party is significant. In Smith v. Maryland, for example, the Supreme Court held that a telephone user has no constitutional privacy interest in the numbers the user dials. This is because the user knows the phone company records dialed numbers, which appear on phone bills. But the Court further noted that most phone books also contained a warning that the phone company "can frequently help in identifying to the authorities the origin of unwelcome and troublesome calls." This explicitly flagged that phone companies might disclose dialing information to the government. Therefore, the Court concluded that "it is too much to believe that telephone subscribers under these circumstances harbor any general expectation that the numbers they dial will remain secret." Smith v. Maryland, 442 U.S. 735, 743 (1979).

When Chatrie enabled Location History on his phone, he first saw a message from Google stating that doing so "saves where you go with your devices." The message also stated that he had the ability to view or delete his location data, and that Google might use the data to "give you more personalized experiences." Chatrie, 107 F.4th at 331 (cleaned up). Arguably, this is the equivalent of the phone book warning given in Smith--though Google did not mention it might disclose the location information "to the authorities." Thus, this may mean that Chatrie could not reasonably have harbored a general expectation that where he went with his cell phone would remain secret.

The government also argued that geofence searches are less intrusive than traditional searches because they often proceed in stages, beginning with anonymized device identifiers. But the government's main argument was that the third-party doctrine applied.

Yet Google Location History may also be considerably more revealing than the cell-site location information at issue in Carpenter. GPS-based application tracking can provide a far more precise and comprehensive record of a person's movements, associations, and routines than ordinary cell-tower records. "Location History can hunt down a user's whereabouts within meters, and even discern elevation, locating the specific floor in a building where a person might be." Chatrie, 107 F.4th 350 (Wynn, J. dissenting) (original emphasis).

IV. The problem of overbroad geofence searches

Despite Chatrie having enabled Location History on his phone, the third-party doctrine may not persuade a majority of the justices. If the third-party doctrine prevails, then obtaining geofence data from companies will fall outside the Fourth Amendment's definition of a search--and therefore the police will not need a warrant to get such location data. Without a warrant there is no judge to rule on whether a geofence request is overbroad under the Fourth Amendment. How broad could geofence requests become?

Amicus briefs are rarely mentioned in Supreme Court opinions, but they can influence the justices' thinking. And in Chatrie, Google filed an amicus brief that stands out. Not for its legal arguments, but because Google attached examples of actual geofence search warrants it had received that it had then challenged in court and that had been held to be overbroad. These provide real-world examples where the police would have obtained thousands of users' historic location data had the police not been constrained by the Fourth Amendment's warrant requirement.

One geofence search "covered nearly all of Aspen, Colorado, including 29 hotels, two ski resorts, the local airport, portions of US Route 82, and the vast majority of homes and businesses in Aspen for three hours in the evening." Brief for Amicus Curiae Google LLC In Support of Neither Party, filed in Chatrie v. United States No. 25-112, at p. 23. Aspen has over 6,000 residents; and including the guests at the 29 hotels, this geofence potentially would have swept up information on perhaps 7,000 people.

A second geofence search "covered nearly 20 square miles over Vail, Colorado. The geofence included nearly every home and business in Vail, Colorado, including 48 hotels, several ski resorts, four churches and two synagogues, and portions of Interstate 70 for two hours in the evening." Id. at p. 24. Vail has over 4,000 residents; and guests from 48 hotels likely would add at least 2,000 more people. The geofence searches of Aspen and Vail also encompassed at least two hospitals.

Google emphasized that a court had granted Google's motion to quash these searches, on the basis that they were overbroad, and that "Google did not produce any data in response to this warrant." Id. But if the third-party doctrine applies to geofence searches, then all these people in Aspen and Vail would likely lack Fourth Amendment protection against government acquisition of that geolocation data from Google, and the police could gather up as much of it as they deemed necessary, without needing a warrant--regardless of whether the people were in their homes, at a place of worship, or at a hospital.

V. Oral argument revealed competing constitutional concerns

The Chatrie oral argument revealed several competing constitutional concerns: the scope of voluntary disclosure under the third-party doctrine, the breadth of modern digital surveillance, and whether users retain a protectable interest in location data held by technology companies.

Several justices appeared concerned that accepting the government's theory would permit sweeping retrospective surveillance without meaningful judicial oversight. Justice Sonia Sotomayor questioned whether users truly consent to pervasive tracking merely by enabling common smartphone services. Chief Justice John G. Roberts focused on the absence of limiting principles, asking what would prevent increasingly expansive geofence requests in the future. Justices Elena Kagan and Ketanji Brown Jackson likewise appeared skeptical that ordinary participation in digital life should automatically eliminate Fourth Amendment protection.

Justices Neil Gorsuch and Clarence Thomas questioned whether users retain a property-like interest in digital information even after companies store it. Their questions suggested possible interest in treating technology companies more like custodians or bailees of user information rather than unrestricted owners of it.

Other justices appeared more receptive to the government's argument that voluntarily enabling Location History meaningfully distinguishes Chatrie from Carpenter. Justice Amy Coney Barrett focused on the significance of affirmative opt-in consent, while Justices Brett Kavanaugh and Samuel Alito emphasized the investigative value of geofence warrants and the extent to which users knowingly exchange personal information for technological convenience.

The Supreme Court is expected to issue its decision in Chatrie in June. Then, we will learn if and how the third-party doctrine applies to geofence searches for digital historic location data.