A federal appeals court has for the first time ruled that law enforcement must have a warrant in order to track a person’s location data from nearby cell phone towers.

“There is a reasonable privacy interest in being near the home of a lover, or a dispensary of medication, or a place of worship, or a house of ill repute,” the three judges of the 11th Circuit Court of Appeals wrote in a unanimous opinion Wednesday. “That information obtained by an invasion of privacy may not be entirely precise does not change the calculus as to whether obtaining it was in fact an invasion of privacy.”

The ruling is a landmark victory for privacy activists.

“This opinion puts police on notice that when they want to enlist people’s cell phones as tracking devices, they must get a warrant from a judge based on probable cause,” said American Civil Liberties Union Staff Attorney Nathan Freed Wessler. “The court soundly repudiates the government’s argument that by merely using cell a phone, people somehow surrender their privacy rights.”

The case was originally brought in Miami by Quartavious Davis, who is serving more than 160 years in prison for several violent armed robberies. Davis appealed after phone location data was used as evidence in his case, but a judge declined to vacate his sentence, finding that the police acted in “good faith” in their investigation.

The U.S. Supreme Court has not yet issued a ruling on the question of law enforcement access to suspect cell phone location data. However, in a 2012 opinion — upon which the 11th Circuit judges based their opinion delivered Wednesday — the court found that using a GPS tracking device to follow a suspect’s location does constitute a search and thus Fourth Amendment considerations apply.

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