James E. “Jeb” Brown, Esq., Shield Public Safety Training, Inc.
What the Supreme Court’s geofence ruling could mean for ALPRs, pole cameras, drones, and the growing ability to reconstruct a person’s movements
On June 29, 2026, the Supreme Court decided Chatrie v. United States, holding that a geofence warrant used to obtain a person’s cell phone location history from Google is a search under the Fourth Amendment. The opinion does not specifically address Automatic License Plate Readers (ALPRs), pole cameras or drones, but its reasoning challenges some of the legal principles courts have traditionally relied upon to uphold the use of these technologies. In the Fourth Circuit, that conflict already has a name: Schmidt v. City of Norfolk, a pending appeal which could become the first circuit level test of what Chatrie means for camera systems departments have already deployed. This article traces that doctrinal line; explains the mosaic and time machine theories driving it; and offers guidance for building programs which can withstand the direction in which the law is moving.
From Katz to Chatrie: The Line Being Redrawn
Modern search doctrine begins with Katz v. United States which asks whether government conduct intrudes on an expectation of privacy which society recognizes as reasonable. For decades, Katz coexisted with the third-party doctrine: a person generally has no privacy interest in information voluntarily conveyed to a third party. United States v. Jones began to disrupt that balance. The Court held that attaching a GPS tracking device to a vehicle constituted a search under the Fourth Amendment because it involved a physical trespass. In separate concurring opinions, several justices went further, warning that continuously tracking a person’s public movements for an extended period — in this case, about a month — could also raise Fourth Amendment concerns because of the detailed picture of a person’s life such monitoring can create. Carpenter v. United States made that concern part of the Court’s holding. The Court concluded that 127 days of cell site records constituted a search because the records gave police an all-encompassing account of a person’s whereabouts, even though the defendant’s carrier possessed the data. Chatrie confirms that Carpenter was not an isolated decision. The government’s request reached back only about two hours, yet the Court found a protected privacy interest and declined to adopt a categorical duration rule. As the Court explained, where the Fourth Amendment applies, it applies regardless of the quality or quantity of information obtained. Duration is now a factor courts weigh, not a threshold on which a short program can rely to avoid the Fourth Amendment altogether.
Commentators call this the mosaic theory. Individually innocuous data points, such as one ping, one plate read or one camera frame, can collectively reveal a portrait of a person’s movements and associations which no single observation could provide. In Leaders of a Beautiful Struggle v. Baltimore Police Department, the en banc Fourth Circuit struck down a citywide aerial monitoring program and emphasized that combining it with tools police already possessed, including ALPR, magnified the constitutional concern. A related time machine concern is that comprehensive and cheaply searchable records let police reconstruct a person’s past after an investigation makes that person relevant, even though officers had no reason to watch the person when the events occurred.
License Plate Readers: Where the Doctrine Stands
Most courts which have considered ALPR directly have declined to find a search, but their reasoning is narrower than is often suggested. The Massachusetts Supreme Judicial Court upheld four bridge cameras in Commonwealth v. McCarthy, while leaving open the possibility that historic ALPR data collected by enough cameras in enough locations could invade a reasonable expectation of privacy. The Ninth Circuit resolved United States v. Yang on standing grounds, with a concurrence cautioning that a warrant might eventually be required if the technology developed toward Carpenter level comprehensiveness. In January 2026, the Eastern District of Virginia upheld Norfolk’s 175 camera network in Schmidt, reasoning that a rolling 21 day retention period kept the system from producing an all-encompassing record. The court nevertheless acknowledged that the system could become too intrusive as camera density increased and upheld it only under the circumstances then presented. This line of cases applies a scale and density analysis, not a categorical rule. Schmidt is now before the Fourth Circuit, with the ACLU and Electronic Frontier Foundation participating as amici. The district court relied in part on a Fourth Circuit Chatrie panel opinion which was later vacated en banc and reversed by the Supreme Court. ALPR is not a cell phone case and stationary cameras trace to an older line of authority holding that drivers ordinarily lack a privacy interest in movements exposed to public view. Chatrie nevertheless weakens the argument that voluntary exposure and short retention alone defeat any privacy interest.
Pole Cameras: A Split Chatrie Has Complicated
Pole camera doctrine is older and the government prevails more often than is sometimes assumed. Eight federal circuits have upheld long-term, warrantless exterior monitoring as conventional technology comparable to a security camera. An older Fifth Circuit decision, United States v. Cuevas Sanchez, found a search where the defendant had fenced the observed area from public view. The First Circuit divided evenly en banc in United States v. Moore Bush over eight months of continuous footage. Three judges reasoned that duration transformed public moments into a comprehensive record which no one would expect to be perfectly preserved for future examination. Many government favorable decisions rely heavily on duration, treating shorter monitoring periods as conventional while expressing greater concern about many months of continuous observation. Chatrie does not resolve that division, but it removes a significant premise from any opinion that treats a shorter period as sufficient by itself. Legal scholars commenting on Chatrie have noted that, because the Court declined to treat the length of surveillance as the deciding factor, it may now be harder to predict how courts will evaluate challenges involving pole cameras used continuously for several months.
Drones: An Already Skeptical Doctrine Meets a Fast-growing Program
Aerial observation doctrine dates to three Supreme Court cases from the 1980s holding that warrantless observation from public airspace generally is not a search because members of the public flying overhead could see the same area. Drones do not fit comfortably within that framework. In Long Lake Township v. Maxon, a Michigan appellate court required a warrant for low altitude, targeted drone observation of a home, reasoning that drones can reach altitudes and intimate spaces which conventional aircraft cannot. Leaders of a Beautiful Struggle remains controlling Fourth Circuit authority on persistent aerial monitoring and provides an important analytical framework for drone programs. According to the Electronic Frontier Foundation’s Atlas of Surveillance and related public reporting, Drone as First Responder programs have expanded rapidly since 2018. Many platforms can be integrated with plate reader and identity linking data which presents the type of data combination the Fourth Circuit identified as a constitutional multiplier. The practical risk is less about one flight than about the record a program accumulates. A drone network with months of retained, searchable footage cross-referenced against an ALPR database begins to resemble the aggregated record which concerned the Court in Carpenter and Chatrie.
A Concrete Illustration: Leonardo’s SignalTrace™ and Multi-sensor Data Fusion
Leonardo S.p.A., through its ELSAG public safety technology business, offers SignalTrace as a capability designed to operate alongside automatic license plate reader systems. Rather than relying exclusively on a camera image and license plate number, SignalTrace adds another layer of information by detecting electronic signals being transmitted by nearby consumer devices.
The technology can detect and develop electronic signatures associated with signals such as Bluetooth®, Wi-Fi and radio frequency identification (RFID). These signatures do not, by themselves, provide an investigator with the name of the person carrying a phone, smartwatch or other device. Instead, the system is designed to recognize when the same electronic signatures, or recurring groups of signatures, appear at different locations and times.
Consider a vehicle which routinely passes an ALPR location while two smartphones and a smartwatch are located inside it. The plate reader provides the vehicle information, while SignalTrace detects electronic signatures associated with devices moving nearby. If substantially the same combination repeatedly appears with that vehicle, the system can establish an association between the vehicle, those device signatures, along with the location and the time of detection. The value comes from recognizing the pattern again later.
For example, if one of those previously observed device signatures subsequently appears near a different vehicle or at another location relevant to an investigation, an investigator may be able to search the historical information and identify the earlier association. Conversely, a recurring combination of device signatures may provide another means of recognizing a vehicle or travel pattern in situations where a usable license plate image was not captured.
Leonardo’s product materials and patents describe capabilities for correlating electronic signatures with license plate records, analyzing movement patterns, identifying devices which repeatedly travel together and developing information about possible routes. In this respect, SignalTrace expands the traditional ALPR model from a record centered primarily on a vehicle and plate number to one capable of correlating several types of observations.
From an investigative standpoint, that additional information can help develop leads when investigators begin with incomplete information. They may know a plate number, a vehicle, an electronic signature, a location, or a recurring group of devices and use the system to search for related observations. SignalTrace therefore does not necessarily require an investigation to begin with the identity of a particular person.
An important distinction is that detecting an electronic signature is not the same as identifying the individual carrying the device. A phone can be borrowed, left inside a vehicle or detected while its owner is merely nearby. Likewise, two devices which repeatedly appear together establish proximity, not necessarily the nature of the relationship between their users. Any association produced by the system remains an investigative lead which must be evaluated and corroborated using other information.
That distinction is also what makes SignalTrace relevant to the developing Fourth Amendment questions discussed here. The constitutional issue is not simply whether an individual plate read or wireless device signature reveals a person’s identity. The larger question is what can be learned when those observations are retained, made searchable and combined over time. A recurring electronic signature which initially contains no name may become considerably more informative when correlated with vehicle registration information, ALPR records, locations, other device signatures, or additional investigative data.
SignalTrace thus provides a useful example of the broader evolution of surveillance technology: Separate pieces of information which reveal relatively little on their own can become more useful – and potentially more revealing – when a system is able to associate them across multiple locations and encounters. For agencies, the technology’s investigative capabilities make questions involving retention, access, data sharing, and the combination of information from different systems particularly important when developing policy.
The Pushback Is Not Only Constitutional
A second, faster moving front has little to do with the Fourth Amendment: state statutory law. California’s ALPR Privacy Act, Civil Code sections 1798.90.5 through 1798.90.55, requires a public usage and privacy policy, access logging and limits on data sharing. The statute authorizes damages of $2,500 for each violation. In Bartholomew v. Parking Concepts, Inc., the California Court of Appeal held in 2026 that failure to publish the required policy can itself support a claim, without a separate data breach or misuse allegation. The California Supreme Court denied review. Other states have considered or enacted restrictions after agencies learned that vendor default settings allowed broader sharing than governing bodies had approved. NPR and local news organizations also reported contract cancellations during 2025 and 2026 involving camera, plate reader and drone platforms.
Building Programs for Where the Law Is Going
None of this requires agencies to abandon ALPRs, pole cameras or drones. The SignalTrace example, likewise, is not a criticism of a particular company or product. The relevant question is whether the agency has built a lawful, transparent and auditable program. The following measures provide a practical compliance framework.
- Retention: Set the shortest period each technology’s purpose is justified and be able to explain why. A short window helps after Chatrie, but no longer guarantees an outcome.
- Sharing scope: Disable default nationwide sharing settings; require case-by-case, documented authorization before another agency can query local data.
- Fusion review: Combining ALPR, aerial platforms, facial recognition, or device-signature add-ons like SignalTrace should get independent Fourth Amendment review before deployment.
- Duration discipline: Avoid open-ended camera and drone deployments; use defined windows with periodic reauthorization.
- Policy and audit trail: Confirm that a compliant and genuinely public usage policy exists and is followed. Under some statutes, the absence of the required policy can itself create liability.
- Contractual control: Vendor agreements should give the municipality, not the vendor, control over every sharing, retention and fusion setting, with audit rights.
- Periodic legal review: Reassess each program’s Fourth Amendment posture annually and after any decision which touches the doctrine directly.
Conclusion
Chatrie is not an ALPR, pole camera or drone case, and it resolves none of those questions directly. It does confirm that the Supreme Court will look beyond the third- party doctrine’s traditional formalities and ask whether a technology allows the government to reconstruct a revealing account of a person’s movements. It also establishes that short duration is not, by itself, a safe harbor. The programs most likely to withstand legal scrutiny will be those designed now with narrow retention, controlled sharing, documented access, periodic review, and careful limits on the combination of data sources.
James E. “Jeb” Brown, Esq., is the cofounder of Shield Public Safety Training, Inc. (shieldpst.org), a national law enforcement legal education organization. He previously served as Supervising Deputy City Attorney for the City of Riverside and as Chief Assistant County Counsel for Riverside County, California, in a career centered on representing and advising law enforcement officers and agencies.
Understanding Chatrie: Geofence Warrants and the Fourth Amendment
Larry E. Holtz, Esq.
Unlike a traditional warrant aimed at a known suspect, a geofence warrant works in reverse. Officers identify a crime location and time period, and a technology company searches its location database for devices which were in, or near, that area. The tool can help identify unknown suspects or witnesses, but it also raises significant Fourth Amendment concerns because it may capture location information for people who happened to be nearby.
In Chatrie v. United States, 609 U.S. ___ (6/29/2026), the U.S. Supreme Court addressed a geofence warrant used to investigate a Virginia bank robbery. The robber entered the Call Federal Credit Union in Midlothian, Virginia, displayed a handgun, threatened bank employees, forced the manager to open the safe, and fled with approximately $195,000. Surveillance footage showed that the robber appeared to be using a cell phone before the robbery, but investigators had no suspect.
Officers obtained a geofence warrant directed to Google. The warrant sought Location History data for phones within a 150 meter radius of the credit union during a one hour window surrounding the robbery. Google’s response eventually identified three users, one of whom was Okello Chatrie. His location data placed him near the credit union shortly before the robbery and showed him leaving the area afterward. Officers later executed search warrants at residences associated with Chatrie and found robbery demand notes, nearly $100,000 in cash and a 9mm pistol. Chatrie pleaded guilty and was sentenced to nearly 12 years in prison.
The Fourth Circuit upheld the conviction, reasoning that obtaining Chatrie’s Google Location History data was not a Fourth Amendment search because he had voluntarily provided the information to Google. The Supreme Court disagreed. Relying heavily on Carpenter v. United States, the Court held that police conduct a Fourth Amendment “search” when they obtain a person’s cell phone Location History data from Google. The Court explained that individuals have a reasonable expectation of privacy in detailed records of their cell phone location, even when that information is held by a third-party technology company.
The Court emphasized that Google Location History may be even more revealing than traditional cell site location information. It can record a phone’s location frequently, pinpoint location with greater precision and even estimate elevation, potentially showing which floor of a building a person entered. The Court also rejected the government’s argument that two hours of location data was too brief to trigger Fourth Amendment protection. Even short-term location tracking can reveal sensitive information, such as visits to a home, doctor, lawyer, religious site, political event, or other private location.
The Court also declined to apply the traditional third-party doctrine. Although Google stored the data, the Court concluded that ordinary smartphone use does not mean a person has surrendered constitutional protection in detailed digital location records.
Importantly, the Court did not decide whether the geofence warrant was valid. Instead, it remanded the case for the lower court to decide whether the warrant was supported by probable cause and described with sufficient particularity. For law enforcement, the practical lesson is clear: Geofence warrants are searches under the Fourth Amendment and must be drafted with careful attention to probable cause, narrow time and location limits, minimization procedures, and particularized standards for moving from anonymized data to identifying a specific user.
It should be noted, however, that Google has now instituted a significant change which apparently insulates Location History data from geofence warrants. In July 2025, years after the geofence warrant used in this case, Google now stores Location History data on individual users’ devices rather than on its own servers. As a result, Google is no longer capable of responding to geofence warrants which seek Location History data.
Larry E. Holtz has served as a Detective Sergeant with the Atlantic City, New Jersey, Police Department; a Deputy Attorney General for the state of New Jersey, and an Assistant County Prosecutor. Presently, Mr. Holtz is a leading author for Blue360° Media, the largest US provider of legal information which is solely focused on serving law enforcement. Mr. Holtz is a certified police trainer and teaches on a regular basis. He is a member of the bar in New Jersey, Pennsylvania and the District of Columbia and is admitted to practice before the federal bar in the District of New Jersey and the Third Circuit.