The Supreme Court agreed Monday to decide its biggest privacy dispute in years, a case that asks whether the authorities need a probable-cause court warrant to access people's mobile phone location history.

"Because cell phone location records can reveal countless private details of our lives, police should only be able to access them by getting a warrant based on probable cause," said Nathan Freed Wessler, a staff attorney with the American Civil Liberties Union. "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."

For years, the authorities have been obtaining data pinpointing the cell towers that a suspect's mobile phone pinged—all without a warrant. That information is then used as evidence showing a suspect's past whereabouts. In the case before the justices, the authorities got 127 days of cell-site information that included 12,898 location points as part of a Detroit robbery investigation.

Police can get this information without a warrant because of the so-called third-party doctrine. That's a legal theory allowing the government to demand companies to provide private information on people if that information is considered a normal business record. Because cell-site data is deemed a business record of the mobile phone companies, the telcos are required to disclose it as part of government investigations, without a probable-cause warrant.

The issue now reaches the Supreme Court, as this method of surveillance has become an important crime-fighting tool following the justices' 2012 ruling that a warrant is needed for the authorities to place GPS trackers on vehicles.

In that decision, however, the court skirted the third-party doctrine issue and instead said that the act of police affixing a GPS device to a vehicle amounted to a trespassing of sorts, so a warrant was needed.

At the time, Justice Sonia Sotomayor said the third-party doctrine has come to a boil. In a concurring opinion, she wrote that the third-party doctrine is "ill-suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks."

The doctrine also provided the legal underpinnings of the National Security Agency's telephone metadata snooping program disclosed by whistleblower Edward Snowden.

There's hope the justices might resolve the cell-site issue in favor of consumer privacy. The justices sided with consumers the last time they ruled on a digital rights case. In 2014, the Supreme Court unanimously held that the authorities generally cannot search the mobile phones of those they arrest unless they have a court warrant.

"Given the increasing use of new forms of electronic surveillance, it's important now more than ever that the Supreme Court steps in to push back against police overreach and clarify the protections of the Fourth Amendment," said Harold Gurewitz, an attorney who, along with the ACLU, represents Detroit robbery suspect Timothy Carpenter.

The cell-site data the authorities got on Carpenter, convicted of six robbery counts, placed him near armed robberies of Radio Shack and T-Mobile stores. A federal appeals court rejected Carpenter's contention that a warrant for the data was required. The Cincinnati-based 6th US Circuit Court of Appeals wrote (PDF) that phone companies must disclose the data if the authorities claim the information is "relevant and material to an ongoing criminal investigation."