The U.S. Supreme Court on Monday heard arguments in a landmark legal case that could redefine digital privacy rights for people across the United States.

The case, Chatrie v. United States, centers on the government’s controversial use of so-called “geofence” search warrants. Law enforcement and federal agents use these warrants to compel tech companies, like Google, to turn over information about which of its billions of users were in a certain place and time based on their phone’s location.

By casting a wide net over a tech company’s stores of users’ location data, investigators can reverse-engineer who was at the scene of a crime, effectively allowing police to identify criminal suspects akin to finding a needle in a digital haystack.

But civil liberties advocates have long argued that geofence warrants are inherently overbroad and unconstitutional as they return information about people who are nearby yet have no connection to an alleged incident. In several cases over recent years, geofence warrants have ensnared innocent people who were coincidentally nearby and whose personal information was demanded anyway, been incorrectly filed to collect data far outside of their intended scope, and used to identify individuals who attended protests or other legal assembly.

The use of geofence warrants has seen a surge in popularity among law enforcement circles over the last decade, with a New York Times investigation finding the practice first used by federal agents in 2016. Each year since 2018, federal agencies and police departments around the U.S. have filed thousands of geofence warrants, representing a significant proportion of legal demands received by tech companies like Google, which store vast banks of location data collected from user searches, maps, and Android devices.

Chatrie is the first major Fourth Amendment case that the U.S. top court has considered this decade. The decision could decide whether geofence warrants are legal. Much of the case rests on whether people in the U.S. have a “reasonable expectation” of privacy over information collected by tech giants, like location data.

It’s not yet clear how the nine justices of the Supreme Court will vote — a decision is expected later this year — or whether the court would outright order the stop to the controversial practice. But arguments heard before the court on Monday give some insight into how the justices might rule on the case. 

‘Search first and develop suspicions later’

The case focuses on Okello Chatrie, a Virginia man convicted of a 2019 bank robbery. Police at the time saw a suspect on the bank’s security footage speaking on a cellphone. Investigators then served a “geofence” search warrant to Google, demanding that the company provide information about all of the phones that were located a short radius of the bank and within an hour of the robbery. 

In practice, law enforcement are able to draw a shape on a map around a crime scene or another place of significance, and demand to sift through large amounts of location data from Google’s databases to pinpoint anyone who was there at a given point in time.

In response to the geofence warrant, Google provided reams of anonymized location data belonging to its account holders who were located in the area at the time of the robbery, then investigators asked for more information about some of the accounts who were near to the bank for several hours prior to the job. 

Police then received the names and associated information of three account holders — one of which they identified as Chatrie.

Chatrie eventually pleaded guilty and received a sentence of more than 11 years in prison. But as his case progressed through the courts, his legal team argued that the evidence obtained through the geofence warrant, which allegedly linked him to the crime scene, shouldn’t have been used.

A key point in Chatrie’s case invokes an argument that privacy advocates have often used to justify the unconstitutionality of geofence warrants.

The geofence warrant “allowed the government to search first and develop suspicions later,” they argue, adding that it goes against the long-standing principles of the Fourth Amendment that puts guardrails in place to protect against unreasonable searches and seizures, including of people’s data.

As the Supreme Court-watching site SCOTUSblog points out, one of the lower courts agreed that the geofence warrant had not established the prerequisite “probable cause” linking Chatrie to the bank robbery justifying the geofence warrant to begin with. 

The argument posed that the warrant was too general by not describing the specific account that contained the data investigators were after.

But the court allowed the evidence to be used in the case against Chatrie anyway because it determined law enforcement acted in good faith in obtaining the warrant.

According to a blog post by civil liberties attorney Jennifer Stisa Granick, an amicus brief filed by a coalition of security researchers and technologists presented the court with the “most interesting and important” argument to help guide its eventual decision. The brief argues that this geofence warrant in Chatrie’s case was unconstitutional because it ordered Google to actively rifle through the data stored in the individual accounts of hundreds of millions of Google users for the information that police were looking for, a practice incompatible with the Fourth Amendment.

The government, however, has largely contended that Chatrie “affirmatively opted to allow Google to collect, store, and use” his location data and that the warrant “simply directed Google to locate and turn over the necessary information.” The U.S. solicitor general, D. John Sauer, arguing for the government prior to Monday’s hearing, said that Chatrie’s “arguments seem to imply that no geofence warrant, of any sort, could ever be executed.”

Following a split-court on appeal. Chatrie’s lawyers asked the U.S. top court to take up the case to decide whether geofence warrants are constitutional.

Justices appear mixed after hearing arguments

While the case is unlikely to affect Chatrie’s sentence, the Supreme Court’s ruling could have broader implications for Americans’ privacy.

Following live-streamed oral arguments between Chatrie’s lawyers and the U.S. government in Washington on Monday, the court’s nine justices appeared largely split on whether to outright ban the use of geofence warrants, though the justices may find a way to narrow how the warrants are used.

Orin Kerr, a law professor at the University of California, Berkeley, whose expertise includes Fourth Amendment law, said in a lengthy social media post that the court was “likely to reject” Chatrie’s arguments about the lawfulness of the warrant, and would likely allow law enforcement to continue using geofence warrants, so long as they are limited in scope.

Cathy Gellis, a lawyer who writes at Techdirt, said in a post that it appeared the court “likes geofence warrants but there may be hesitance to fully get rid of them.” Gellis’ analysis anticipated “baby steps, not big rules” in the court’s final decision.

Although the case focuses much on a search of Google’s location databases, the implications reach far beyond Google but for any company that collects and stores location data. Google eventually moved to store its users’ location data on their devices rather than on its servers where law enforcement could request it. The company stopped responding to geofence warrant requests last year as a result, according to The New York Times.

The same can’t be said for other tech companies that store their customers’ location data on their servers, and within arm’s reach of law enforcement. Microsoft, Yahoo, Uber, Snap, and others have been served geofence warrants in the past.