Government GPS tracking almost always requires a warrant based on probable cause, whether officers physically attach a device to your car or pull historical location records from your wireless carrier. Two Supreme Court decisions set that baseline: United States v. Jones in 2012 for physical trackers, and Carpenter v. United States in 2018 for cell-site location information. The warrant requirement has real exceptions, though, and several newer tracking methods sit in legal gray areas where no clear rule has been settled.
Physical GPS Devices on a Vehicle
Attaching a GPS tracker to your car is itself a Fourth Amendment search. In Jones, agents installed a device on a suspect’s Jeep without a valid warrant and tracked him for 28 days. The Supreme Court held that the government’s physical intrusion on a constitutionally protected “effect” for the purpose of gathering information is a search, reviving a trespass-based reading of the Fourth Amendment that many scholars had assumed was gone.1Legal Information Institute. United States v. Jones
Federal officers work under Rule 41 of the Federal Rules of Criminal Procedure when they seek a tracking-device warrant. The rule sets hard limits:
- The warrant lasts no more than 45 days from issuance. Extensions require good cause and are capped at another 45 days each.
- The device must be installed within 10 calendar days of the warrant being issued.
- Installation must occur between 6:00 a.m. and 10:00 p.m. unless a judge authorizes nighttime installation for good cause.
- After the authorized period ends, officers must return the warrant to the issuing judge.
The rule also requires the warrant to identify the specific person or property being tracked and to designate which judge receives the return.2Legal Information Institute. Rule 41 – Search and Seizure A separate statute, 18 U.S.C. § 3117, lets a court’s tracking order reach beyond its own district as long as the device was installed inside it.3Office of the Law Revision Counsel. 18 USC 3117 – Mobile Tracking Devices
Historical Cell-Site Location Data
Your phone pings nearby cell towers constantly, and carriers keep those records as part of their normal business. Prosecutors used to obtain that data with a court order under the Stored Communications Act, which required only “reasonable grounds” instead of probable cause. Carpenter v. United States ended that shortcut. Acquiring historical cell-site location information (CSLI) is a Fourth Amendment search that requires a warrant supported by probable cause.4Supreme Court of the United States. Carpenter v. United States
The Carpenter case involved 127 days of data, roughly 13,000 location points for one person. The Court described phones as “almost a feature of human anatomy” and treated CSLI as an intimate, comprehensive record of movement that would have required an army of agents to compile through traditional means.
The opinion is deliberately narrow. The Court did not decide the rules for real-time CSLI, tower dumps (bulk downloads of every device that connected to a given tower), conventional camera surveillance, or national security collection.5Justia. Carpenter v. United States The traditional third-party doctrine remains intact for most other business records. What set CSLI apart, in the Court’s reading, was its pervasiveness, its automatic generation without any affirmative act by the user, and the depth of private life it exposes.
Cell-Site Simulators (Stingrays)
Cell-site simulators, often called stingrays or IMSI catchers, mimic cell towers so that nearby phones connect to them and reveal identifying information and location. Because law enforcement operates the device directly, a stingray can capture data from every phone in range, not just a target’s.
In September 2015, the Department of Justice adopted a policy requiring federal agents to obtain a probable-cause warrant before using a cell-site simulator, except in exigent circumstances. The policy conceded that the older practice of relying only on pen-register orders was not enough. Even under the exigency exception, agents must still comply with the Pen Register Statute and get judicial authorization after the fact.6U.S. Department of Justice. DOJ Cell-Site Simulator Policy Several states have their own warrant requirements, and lower courts have not converged on whether warrantless stingray use violates the Fourth Amendment.
Geofence Warrants
A geofence warrant reverses the usual sequence. Law enforcement defines an area and a time window, then compels a technology company to identify every device that was present. Because the search starts with a place rather than a person, it inevitably sweeps in bystanders.7Congress.gov. Geofence Warrants and the Fourth Amendment
Federal courts have split on whether geofence warrants satisfy the Fourth Amendment’s particularity requirement, and the Supreme Court has agreed to hear Chatrie v. United States, which challenges the practice directly. Practical conditions have already shifted: in late 2023 Google began storing location data on users’ devices instead of on company servers, which makes broad geographic sweeps against Google’s database functionally impossible and pushes investigators back toward targeted, device-specific warrants.
When a Warrant Is Not Required
Several recognized exceptions let the government track location without going to a judge first. They are supposed to be narrow, but each covers meaningful ground.
Exigent Circumstances
When a life is in immediate danger, evidence is about to be destroyed, or a suspect is actively fleeing, officers can begin tracking without waiting for a warrant. Courts test the claimed emergency after the fact. If it does not hold up, the evidence is suppressed.
Consent and Border Searches
Voluntary, informed consent removes the warrant requirement. So does the border-search doctrine: at the national border and its functional equivalents, such as international arrival areas in airports, authorities have broad search authority rooted in national sovereignty. Routine inspections require neither a warrant nor individualized suspicion, though more intrusive searches may require reasonable suspicion.
Parolees and Probationers
People on parole or probation have sharply diminished privacy rights. In Samson v. California, the Supreme Court held that the Fourth Amendment does not bar suspicionless searches of parolees, reasoning that the state’s interest in supervising released individuals outweighs their reduced privacy expectations.8Justia. Samson v. California Several federal circuits have extended that logic to uphold warrantless GPS tracking of parolees.
Court-Ordered Ankle Monitors
GPS monitoring imposed as a condition of pretrial release, probation, supervised release, or sex-offender registration is a different framework entirely. Federal courts can require electronic monitoring under 18 U.S.C. § 3563, though only as an alternative to incarceration.9Office of the Law Revision Counsel. 18 USC 3563 – Conditions of Probation The federal probation system uses non-removable, waterproof ankle devices that track location through GPS satellites, cellular towers, and Wi-Fi; participants charge the device daily.10United States Courts. Chapter 3 – Location Monitoring, Probation and Supervised Release
The Supreme Court confirmed in Grady v. North Carolina that attaching a GPS device to a person’s body without consent is a Fourth Amendment search, even for a convicted sex offender in a state monitoring program. The Court did not strike the program down. Whether such a search is reasonable turns on the totality of the circumstances, including the purpose of the monitoring and how deeply it intrudes on legitimate privacy interests.11Justia. Grady v. North Carolina Courts have generally upheld mandatory GPS monitoring of sex offenders as reasonable, and more than 20 states require it for certain categories of offenses, with several mandating lifetime tracking for the most serious.
The Commercial Data Loophole
The biggest gap in the warrant framework is not a courtroom exception. It is the open market. Data brokers aggregate GPS-quality location information from mobile apps, and federal agencies buy it. The legal theory is that users technically consented to collection through app terms of service, so purchasing the data avoids Fourth Amendment scrutiny. No warrant, no probable cause, no judge involved.
Agencies can buy detailed movement histories for thousands of people at a time, obtaining the kind of comprehensive surveillance that would clearly require a warrant if pulled from a carrier or gathered by a physical tracker. Congress has tried to close the gap. The Fourth Amendment Is Not For Sale Act, introduced in the 118th Congress as H.R. 4639, would bar federal agencies from purchasing data they would otherwise need a warrant to obtain.12Congress.gov. Fourth Amendment Is Not For Sale Act The bill was reintroduced in the 119th Congress as part of broader surveillance reform. As of early 2026, no version has been signed into law.
Automatic License Plate Readers
Automatic license plate readers (ALPRs) mounted on patrol cars, streetlights, and overpasses photograph every passing plate and log the time and location. Over time, the aggregated data functions much like GPS tracking of a vehicle, without any device ever being attached.
No federal statute regulates ALPR use or sets retention limits. About 16 states have their own ALPR laws, with retention periods running from 21 days to three years. In states without legislation, agencies set their own policies, and some retain the data indefinitely. Courts have not definitively decided whether long-term aggregation of ALPR data triggers the concerns the Supreme Court identified in Carpenter, though the reasoning of that decision points in that direction: months or years of plate reads compile the same kind of comprehensive movement record that the Court found constitutionally significant.
What Happens If Tracking Was Unlawful
The main remedy for illegal government tracking is suppression. A defense attorney files a motion to suppress, and if the judge finds the tracking violated the Fourth Amendment, the location evidence cannot be used at trial. That often guts the prosecution’s case, because GPS data is frequently the linchpin that places a defendant at a scene or establishes a pattern of movement.
Suppression can reach further than the tracking data itself. Under the fruit-of-the-poisonous-tree doctrine, evidence discovered only because of the illegal tracking may also be excluded, including witnesses identified through the data, physical evidence found using it, or probable cause built on it for other searches. Exceptions apply when the evidence would have been inevitably discovered through lawful means or came from a genuinely independent source, and prosecutors bear the burden of proving those exceptions.
On the civil side, 42 U.S.C. § 1983 lets you sue government officials who violated your constitutional rights while acting in their official capacity.13Office of the Law Revision Counsel. 42 U.S. Code 1983 – Civil Action for Deprivation of Rights Qualified immunity shields individual officers unless the right violated was “clearly established” at the time of the conduct. After Jones and Carpenter, the warrant requirement for GPS tracking is about as clearly established as Fourth Amendment law gets.