Cops need a warrant to search your cell phone's location history, Supreme Court rules

The Supreme Court just ruled that cops need a search warrant to get information about where people have been from their cell phones.

The 5-4 decision, written by Chief Justice John Roberts, sets a strong legal limit on how much of your digital data the government can access. But the justices also stressed that these limits apply only to the type of data at question in the case: historical location information. The justices made clear they weren’t weighing in on real-time location records or data related to foreign affairs or national security.

Even so, the ruling is a strong rebuke of the government's encroachment on technological advances.

"Much like GPS tracking of a vehicle, cell phone location information is detailed, encyclopedic, and effortlessly compiled,” the Chief Justice wrote in his majority opinion. “Only the few without cell phones could escape this tireless and absolute surveillance.”

The ACLU brought the case, Carpenter v. U.S., on behalf of Timothy Carpenter, who was arrested for a series of robberies around Detroit largely because his cell phone location data put him within two miles of the crimes. (Some of the robberies were, ironically, at cell phone stores.) The FBI didn’t get a warrant for Carpenter’s location data — because back then, it wasn’t required to.

READ: How the cops can hack into your cell phone without a warrant

Cell-site location information (CSLI) is a record of everywhere your cellphone, and by extension, you, have been. It pieces together a map that can construct a detailed portrait of your life: where you eat, work, study, shop, pray, or even if you’re having an affair.

But until now, there wasn’t a federal directive to protect those records under the Fourth Amendment, which guards against warrantless searches and seizures, because users voluntarily submit the information to a third party: their cell service provider. It’s a caveat to the Fourth Amendment known as the “third-party doctrine.”

Arguments in Carpenter centered to a great extent around whether the third-party doctrine holds up in the 21st century, when disclosing your personal data to third-party companies is nearly unavoidable. But the court wrote Friday that there's a “world of difference” between location data and the types of data the doctrine originally applied to.

Facebook — which is currently under investigation for how it handles user privacy — filed a joint brief in the case alongside other major tech firms. The brief officially argued for neither side but did note that “rigid rules” like the third-party doctrine don’t make sense when applied to digital technologies, and that the government should develop a more nuanced view of what kind of content law enforcement can scoop up without a warrant.

Cover image: A driving instructor supervising a pupil was among 261 people caught illegally using a mobile phone after tougher penalties were introduced. (Barry Batchelor/PA Wire URN:30546694/Press Association via AP Images)