WASHINGTON, D.C. — The U.S. Supreme Court on Monday heard arguments over whether geofence warrants, which allow police to access large tech firms' databases to identify users who were near a crime scene, violate the Fourth Amendment. The technique permits the government to draw a virtual boundary around a geographic area and, with a warrant, compel a tech company to search its data to identify users within that boundary at the time of the crime.

The case before the justices arose from the armed robbery of a bank in Midlothian, Virginia, in which the robber fled with $195,000. After two months without identifying a suspect, police applied for a geofence warrant seeking Google cell phone location data for the area around the bank. A state magistrate judge found probable cause and issued a warrant authorizing disclosure of Google location data for an area about three football fields around the bank for one hour before and after the robbery.

The warrant relied on Google's location history feature, which recorded users' locations every two minutes on average using multiple data sources to pinpoint the location of active cell phones. At the time the case began in 2019, about one-third of Google users, approximately 500 million people, had voluntarily enabled the feature. Google stored the data in its cloud and provided it to law enforcement only upon presentation of a warrant.

Google initially identified 19 unnamed cell phone users as potential suspects, then negotiated with law enforcement to reduce the request to nine and then to three users before disclosing those three identities. One of the three, Okello Chatrie, was arrested. The other two were innocent bystanders. "This was a little bit of an investigative lottery ticket when they had no other way of finding a suspect," said Stanford law professor Orin Kerr.

The Trump administration argued to the Supreme Court that cellphone users who opted into Google's location history feature waived any reasonable expectation of privacy, and that because the defendant did not take steps to protect his location information, he had no right to privacy whether or not a warrant was obtained. Justice Department lawyer Michael Dreeben acknowledged the court's prior direction in digital privacy cases. "One can sum up those cases by saying that when the court was asked to apply analog-era precedents to digital realities, it has uniformly favored privacy interests rather than extending precedents that allowed government searches," he said. Dreeben also noted the range of activities the location data could expose. "They may have been going to church. They may have been seeing a psychiatrist. They may have been visiting a lover," he said.

Attorney Adam Unikowsky, arguing against the warrant, invoked the country's founding era. "At the Founding, people absolutely despised general warrants that would allow the police to search every single person's house without any suspicion," he said. "So we argue in this case that the warrant was unconstitutional because it allowed the government to search every single person's account for evidence of a crime, which is a little bit like searching every single person's house," Unikowsky said.

After the January 6 Capitol riot, federal law enforcement officers used geofencing to distinguish demonstrators who clashed with police and invaded the Capitol from those who were peaceably walking on the Capitol grounds.