In a major decision on Friday, the federal Fifth Circuit Court of Appeals held that geofence warrants are “categorically prohibited by the Fourth Amendment.” Closely following arguments EFF has made in a number of cases, the court found that geofence warrants constitute the sort of “general, exploratory rummaging” that the drafters of the Fourth Amendment intended to outlaw. EFF applauds this decision because it is essential that every person feels like they can simply take their cell phone out into the world without the fear that they might end up a criminal suspect because their location data was swept up in open-ended digital dragnet.

The new Fifth Circuit case, United States v. Smith, involved an armed robbery and assault of a US Postal Service worker at a post office in Mississippi in 2018. After several months of investigation, police had no identifiable suspects, so they obtained a geofence warrant covering a large geographic area around the post office for the hour surrounding the crime. Google responded to the warrant with information on several devices, ultimately leading police to the two defendants.

On appeal, the Fifth Circuit reached several important holdings.

First, it determined that under the Supreme Court’s landmark ruling in Carpenter v. United States, individuals have a reasonable expectation of privacy in the location data implicated by geofence warrants. As a result, the court broke from the Fourth Circuit’s deeply flawed decision last month in United States v. Chatrie, noting that although geofence warrants can be more “limited temporally” than the data sought in Carpenter, geofence location data is still highly invasive because it can expose sensitive information about a person’s associations and allow police to “follow” them into private spaces.

Second, the court found that even though investigators seek warrants for geofence location data, these searches are inherently unconstitutional. As the court noted, geofence warrants require a provider, almost always Google, to search “the entirety” of its reserve of location data “while law enforcement officials have no idea who they are looking for, or whether the search will even turn up a result.” Therefore, “the quintessential problem with these warrants is that they never include a specific user to be identified, only a temporal and geographic location where any given user may turn up post-search. That is constitutionally insufficient.”

Unsurprisingly, however, the court found that in 2018, police could have relied on such a warrant in “good faith,” because geofence technology was novel, and police reached out to other agencies with more experience for guidance. This means that the evidence they obtained will not be suppressed in this case.

Nevertheless, it is gratifying to see an appeals court recognize the fundamental invasions of privacy created by these warrants and uphold our constitutional tradition prohibiting general searches. Police around the country have increasingly relied on geofence warrants and other reverse warrants, and this opinion should act as a warning against narrow applications of Fourth Amendment precedent in these cases.