Geofence Warrants and the Fourth Amendment: What the Supreme Court’s Chatrie Decision Means for Your Privacy

On April 28, 2026, the United States Supreme Court heard oral arguments in United States v. Chatrie — the most consequential Fourth Amendment case involving location privacy in years. The central question: does the Constitution require a warrant before police can use a “geofence warrant” to obtain the location history of every cell phone near a crime scene?

The case is a direct sequel to Carpenter v. United States (2018), the landmark 5-4 ruling that government access to historical cell phone location data requires a warrant. But Chatrie goes further — it asks whether even that protection is enough when police don’t have a suspect at all, only a location where a crime occurred.

What Is a Geofence Warrant?

A geofence is a virtual perimeter drawn around a geographic area. Law enforcement uses geofence warrants — also called “reverse location warrants” — to compel a company, almost always Google, to identify all devices that were present within a defined location during a specified time window.

The key word is reverse. Traditional search warrants work like this: police identify a suspect, then obtain a warrant to search that person’s property or data. Geofence warrants invert this: police have no suspect, only a crime scene. They ask Google to search its entire reserve of user location data — stored in a database called Sensorvault — to find everyone whose phone pinged a cell tower near the crime scene.

In the Chatrie case, police were investigating a bank robbery in Midlothian, Virginia. They had no suspect and no useful surveillance footage. They served a geofence warrant on Google. The resulting data narrowed the list of potential suspects to a handful of devices. Timothy Ivory Carpenter — who had no prior record — was eventually convicted based partly on this evidence.

The Technology Behind It: How Your Phone Tracks You

Understanding why geofence warrants are so invasive requires understanding how cell phone location tracking works. There are four primary mechanisms:

GPS satellites provide the most precise location data — often accurate to within a few meters. Your phone’s GPS receiver triangulates your position using signals from satellites in orbit. This data is typically processed on-device.

Cell towers triangulate your position based on which towers your phone connects to. Every time your phone pings a cell tower (which happens constantly to maintain network connectivity), the carrier knows approximately where you are. This is called Cell Site Location Information, or CSLI.

Wi-Fi access points provide location data based on the MAC addresses of nearby routers. Google’s Street View cars mapped Wi-Fi networks worldwide, creating a massive database that can pinpoint your location based on which access points your phone detects.

Bluetooth beacons are used for very precise indoor positioning — increasingly common in retail environments, airports, and stadiums.

Google’s Sensorvault stores this data in aggregate. When you enable “Location History” on your Android device or use Google Maps while signed in, Google records your movements in detail. This is the database that geofence warrants target. According to Google’s own disclosures, geofence warrants have comprised up to 25% of all warrants the company receives each year.

Carpenter v. United States: The 2018 Foundation

In Carpenter v. United States (2018), the Supreme Court ruled 5-4 that the government must obtain a warrant before accessing historical CSLI. Chief Justice John Roberts wrote in the majority opinion that cell phone location data is fundamentally different from other business records because it creates a “comprehensive record of the user’s whereabouts” that reveals “private affairs, information, and facts that the Government could not otherwise obtain without a physical intrusion.”

The Court rejected the third-party doctrine — the legal principle that information voluntarily shared with a third party (like a bank or phone company) receives no Fourth Amendment protection. Roberts wrote: ” cell phone location records reveal the privacies of life. . . . When the Government tracks the location of a cell phone it achieves near perfect surveillance, as if it had implanted a microprocessor in every person’s body.”

But Carpenter was careful to call its holding “narrow.” It addressed only historical CSLI. And the Court specifically left open the question of whether more generalized location data — collected without a suspect in mind — would receive the same protection.

The Chatrie Case: The Reverse Search Problem

Geofence warrants take the reverse approach that Carpenter explicitly declined to fully resolve. In Chatrie, the government didn’t seek data about a specific person. It asked Google to identify every device in an area — sweeping in hundreds of innocent people who happened to be near the bank on the day of the robbery.

The Fourth Circuit ruled this unconstitutional in 2023, with Senior Judge Roger Gregory writing that the warrant was “the very definition of a general warrant” — the precise practice the Fourth Amendment was designed to prohibit. The government appealed, and now the Supreme Court is deciding the question.

During oral arguments on April 28, 2026, justices expressed deep skepticism about the technique. Justice Elena Kagan pressed the government’s position, noting that the approach was “a kind of fishing expedition that could ensnare lots of people.” Chief Justice John Roberts questioned whether a warrant that implicates hundreds of uninvolved people can ever be “reasonable” under the Fourth Amendment.

The government argues that Carpenter’s narrow holding doesn’t extend to geofence warrants because police are still obtaining a warrant — just a warrant targeting a location rather than a person. They argue this is no different from a traditional perimeter search (like setting up a police line) and that requiring a warrant for every investigative technique would handcuff law enforcement.

Google’s Self-Help: Ending Its Own Surveillance Machine

While courts debate, Google has quietly made geofence warrants significantly harder to execute. In December 2023, Google announced major changes to how it handles Location History data:

• On-device storage by default: Location History data will now be stored on your device rather than in Google’s cloud, by default. Google physically cannot produce data it doesn’t have in its servers.
• Three-month auto-deletion: Previously, Google retained Location History data for at least 18 months. The new default deletes it after three months.
• End-to-end encrypted cloud backups: If users opt to back up to Google Cloud, that data will be encrypted so that Google cannot read it — meaning Google couldn’t produce it even if served with a valid warrant.

EFF called these changes “fantastic news for users” and said they could “effectively mean the end of geofence warrants.” The timing is notable: Google’s changes went into effect in June 2024, and they may render the Supreme Court’s ruling less consequential for Google data than it would have been a year earlier.

But other companies still hold vast reserves of location data. And even if Google can’t easily comply with geofence warrants, the legal precedent the Court sets will apply to all location data — from other tech companies, cell carriers, and any entity that collects where you are.

Privacy Protection: What You Can Actually Do

Beyond hoping the Supreme Court rules correctly, there are concrete steps that meaningfully reduce your location exposure:

Turn off Location History: Go to myaccount.google.com/activitycontrols and pause Location History. This is the single highest-impact change. Your phone will still track you locally, but Google won’t upload it to Sensorvault. Note: this doesn’t affect real-time law enforcement requests (which use different legal authority).

Use an iPhone with Apple’s Advanced Data Protection: iOS stores most iCloud data with end-to-end encryption that even Apple cannot access. Enable ADP in Settings → Apple ID → iCloud → Advanced Data Protection.

Review app permissions: Most apps request location access far more broadly than they need. Set location permissions to “While Using” rather than “Always.” Regularly audit which apps have location access at Settings → Privacy → Location Services.

Disable Wi-Fi scanning: Your phone constantly scans for nearby Wi-Fi networks, generating location data even when Wi-Fi is off. Disable this in Settings → Privacy → Location Services → System Services → Wi-Fi Networking.

Use privacy-focused alternatives: DuckDuckGo for search, Signal for messaging, Firefox with enhanced tracking protection for browsing. Each reduces the ecosystem of data collected about you.

Use a VPN: A quality VPN (Mullvad, ProtonVPN, IVPN) masks your IP address and encrypts traffic, making it significantly harder for your ISP and websites to track you. Not location-perfect, but a meaningful layer.

Airplane mode as a privacy tool: When you’re somewhere you don’t want tracked, airplane mode is the only 100% effective option. Your phone stops pinging cell towers, stops sharing GPS, and goes dark.

The Stakes

The Chatrie case is about more than one bank robbery in Virginia. The legal scholars who filed an amicus brief put it starkly: a ruling in favor of geofence warrants could “unleash a much broader wave of similar reverse searches.” If police can constitutionally demand that Google identify everyone within 500 feet of any crime scene, the logical extension is a dragnet that makes the Fourth Amendment’s guarantee against unreasonable searches largely meaningless in the digital age.

On the other side, prosecutors credit geofence warrants with solving cold cases where surveillance cameras missed suspects’ faces, and with identifying participants in the January 6 Capitol attack and pipe bomb investigations. These are not trivial public safety interests.

The Supreme Court is expected to issue its decision by the end of June 2026. Whatever it rules, the case will define the boundaries of location privacy for the smartphone era — and by extension, for the age of ubiquitous surveillance that technology has made possible.

Sources: CGTN (April 28, 2026), EFF DeepLinks, Congress.gov CRS Report LSB11274, Oyez.org (Carpenter v. United States, 585 U.S. 296, 2018), Google Blog, Fourth Circuit opinion in United States v. Chatrie (2023).