The Supreme Court on Monday ruled that police use of location history data pulled from individuals’ phones by tech companies should be considered a Fourth Amendment search and requires a warrant.

The decision is a significant win for privacy and civil liberties advocates who have long held that so-called geofence searches are unconstitutional or at least should be more heavily scrutinized and narrowed. Geofence searches occur when police ask tech companies to produce a list of every phone located in a particular area during a specific time frame, allowing police to pinpoint potential suspects when they have none.

The case centers on Okello Chatrie, a Virginia man who was charged with bank robbery in 2019 after police nabbed him by using Google location history records. While police had a warrant for the search in this case, a lower court ruled that a warrant wasn’t needed at all.

Chatrie’s lawyers challenged that contention, arguing that the search was unreasonable and should not be allowed even with a warrant.

The high court on Monday sent the case back to the U.S. Court of Appeals for the Fourth Circuit for a ruling on whether the Chatrie warrant was reasonable, sufficiently narrowly tailored and otherwise constitutional. The appeals court could now set strict parameters for when and how geofence warrants are executed.

In addition to establishing that geofence searches require warrants, the court also was skeptical of the government’s position that its search was protected by third-party doctrine, an argument law enforcement has made to defend geofence searches, asserting that because individuals choose to share information with Google it is no longer private.

“The big deal is that the court is saying that when a person uses their cellphone in the way people in modern society use a phone, they don't forfeit their Fourth Amendment rights,” Greg Nojeim, director of the Security and Surveillance Project at the Center for Democracy and Technology, said in an interview.

“The court also dealt a strong blow against the legal doctrine that says if you share information with a third party, such as Google, Apple or Microsoft, the government can compel the disclosure of your information without a warrant,” Nojeim added. “The court is removing brick by brick the foundation of this third-party doctrine.” 

While Google no longer stores location history, making it impossible for law enforcement to obtain it, a host of other companies track and store user location data, including Uber, Lyft and Apple. The decision therefore will have a big impact on law enforcement, which sometimes does not use warrants to compel big tech companies to disclose such data.

Had the court ruled that geofence searches are not protected by the Fourth Amendment, experts predicted a surge in law enforcement use of the tool as well as more aggressive use of other kinds of reverse searches such as keyword inquiries to see lists of names searching specific terms on Google. 

“Chatrie is a major win for Fourth Amendment privacy,” George Washington University law professor Andrew Guthrie Ferguson said via email. “In requiring a warrant to obtain location data from your cellphone, the Supreme Court upgraded the Fourth Amendment to meet the digital age.”

Ferguson, also the author of the book Your Data Will be Used Against You, added that the court’s flat rejection of the government’s argument that location data can’t be collected without a judicial warrant sends a “clear signal that it treats digital privacy seriously.”

'Inquisitive eyes of the government'

In a 6-3 vote, the justices held that searching someone’s Google location history is akin to searching private papers and journals, which is expressly prohibited under the Fourth Amendment absent a warrant.

“Google users regularly employ Location History as a personal journal,” Justice Elena Kagan wrote for the majority. “In that way, Location History resembles other private materials — e.g., emails, documents, photographs, or calendars — that even if stored on Google’s servers, a user reasonably views as his own and expects to be shielded from the ‘inquisitive eyes’ of the government.”

The opinion noted that Google repeatedly prompts users to turn on location history and even cautions Android users that their phone will not “work correctly” with it turned off. 

Location history also remains active regardless of whether the user has a Google app open and even when a phone is not in use, the opinion said, noting that even if the user deletes the app for which they turned on location history, Google continues to capture movement history unless a user “affirmatively stops it.”

The precision of location history searches as well as the fact that police can make them retroactively is also an important consideration, the opinion said, noting that location history pinpoints location within around twenty meters, records it about every two minutes and can even see what floor of a building an individual is on by capturing elevation.

“The exposure of that information to Google is merely what happens when a user avails himself of one of the services on his cell phone,” the opinion said. “The Government’s argument that generating Location History… is a voluntary choice is meritless. That argument ignores how and why Google users turn on Location History.”

General warrants

Chatrie’s lawyer had argued for the court to reach a more expansive decision, outlawing geofence searches entirely.

Geofence searches should be considered general warrants, which are unconstitutional, Chatrie’s lawyer, Adam Unikowsky, told Recorded Future News in May. 

A general warrant allows the police to search large groups of people for evidence of a crime without probable cause. Before the Declaration of Independence was written, the authorities used general warrants to search private papers of large numbers of people, usually searching for records relating to tax payments.

General warrants don’t name places to be searched or things to be seized. They simply allow police the authority to “rummage through people's possessions,” Unikowsky said.

Geofence searches that allow police to search large numbers of phone owners’ location histories, exposing people who have nothing to do with a crime to police scrutiny, constitutes a general warrant, Unikowsky said.

“We understand the warrant to search every single person’s Google account, and we're talking about tens of millions here, is akin to a general warrant, which authorized the search of thousands of houses for evidence,” Unikowsky said.