Washington, D.C - The Electronic Frontier Foundation (EFF) urged the U.S. Supreme Court today to curb law enforcement’s expansive tracking of suspects’ cell phones, arguing that police must get a warrant before collecting the detailed location data that all phones generate as part of their routine functioning.

The defendants in U.S. v. Carpenter were convicted after hundreds of days of location data collected from their wireless carriers associated them with a string of armed robberies. But investigators obtained those location records through a lower legal standard than needed for a warrant, relying on the “third-party doctrine”—an outdated legal standard that says if you voluntarily give certain information to entities like banks or the phone company, you have no expectation of privacy in the data.

“The Supreme Court developed the third-party doctrine at a time when everyone used rotary-dial, land-line phones, which couldn't reveal very much about the people who used them,” said EFF Senior Staff Attorney Jennifer Lynch. “The location data our cell phones generate now is much more detailed. As cell phones connect to cell towers and antennas hundreds of times a day, it creates a non-stop flow of information on everywhere we travel—revealing things like when we're at home, whether we're seeing a therapist, where we worship, or what kind of political meetings we might attend. This is far too sensitive information to obtain without a warrant based on probable cause.”

Judges in several states and some federal courts have already recognized that the third-party doctrine should not apply to cell site location data. Meanwhile, in two major recent decisions, the Supreme Court found that modern technology requires updated interpretations of privacy law in order to safeguard constitutional rights. In 2014, the court held that the astounding amount of sensitive data stored on smartphones requires police to obtain a warrant before accessing data on an arrestee’s device. And in a landmark 2012 decision, the court decided that using a GPS tracking device on a suspect’s car is a search under the Fourth Amendment. As it’s impossible to use mapping services, fitness trackers, or many other technologies without sharing data with third-parties, extending these decisions is critical to preserving privacy in the 21st century.

 “Taking advantage of everyday conveniences shouldn’t mean that we have to relinquish our constitutional rights,” said EFF Staff Attorney Andrew Crocker. “We’ve seen the Supreme Court move in the right direction in these cases, and we hope they continue that trend here.”

For our amicus brief in U.S. v. Carpenter:

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