The Supreme Court has agreed to hear its first cell phone location data case.

At issue is whether police need a warrant based on probable cause before accessing cell phone location records from wireless carriers. The American Civil Liberties Union (ACLU), which is serving as co-counsel, argues that without a warrant, law enforcement is infringing on a defendant's Fourth Amendment right to be free from unreasonable search and seizure.

"Cell phone location records can reveal countless private details of our lives," ACLU Staff Attorney Nathan Freed Wessler said in a statement. "The time has come for the Supreme Court to make clear that the longstanding protections of the Fourth Amendment apply with undiminished force to these kinds of sensitive digital records."

The ACLU is representing Timothy Carpenter, who was convicted of robbery in Detroit, based in part on months' worth of phone location records the government obtained in 2011 without a probable cause warrant. The records covered 127 days, revealing 12,898 separate points of location data.

"Carpenter's call records reveal that over the course of four months, his phone was located in more than 200 separate cell tower sectors," the ACLU said. "These records provide a very detailed accounting of everywhere he went."

Carpenter appealed his case to the Sixth Circuit Court of Appeals, which ruled against him 2–1. Now the Supreme Court will address the topic.

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The issue has come up time and again in the court; as the ACLU notes, the Supreme Court declined to hear a similar case in 2015.

Last year, the 4th US Circuit Court of Appeals in Richmond, Virginia, ruled that law-enforcement officials do not need to obtain a warrant before tracking a person's location via wireless carriers. The court found that location data is already delivered to a third party—in this case, the carriers—and therefore doesn't require a warrant if data is readily accessible.

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