It’s a funny thing about the 21st century: Nearly all of us carry location trackers on us, voluntarily, every single place we go. They’re our phones, and we carry them with us when we shop, while we work, while we exercise, while we sleep, and even when we use the bathroom. And that leaves an incredibly valuable, intimate trail of location data that businesses use basically however they want. But as far as your legal rights are concerned, is that personal data actually private?
The Supreme Court agreed today to hear arguments in a case seeking to sort out exactly that question.
The case, Carpenter v United States, centers on a Michigan man, Timothy Carpenter, who was convicted of committing robberies around Detroit in 2011.
As part of that investigation, law enforcement obtained several months’ — 127 days — worth of cell phone location records on their suspect. Those records, the ACLU explains, held nearly 13,000 separate points of location data.
Even if you keep your phone’s GPS disabled, the device itself sends back approximate location data to your carrier based on which signal tower(s) it is able to reach. That data seemed to put the man in the general vicinity of several of the stores that were robbed.
MORE: Should Police Need a Warrant to Obtain Your Cellphone Location Data?
But Carpenter appealed his conviction to the Sixth Circuit, arguing that since law enforcement had not first obtained a search warrant for that phone location data, it was an invalid search in violation of his Fourth Amendment rights.
The court, however, ruled that since the information is basically metadata that has to exist as part of doing business, that it’s not yours and the cops don’t need a warrant.
“Those records say nothing about the content of any calls,” the Sixth Circuit ruled against Carpenter.
“Carriers necessarily track their customers’ phones across different cell-site sectors to connect and maintain their customers’ calls. And carriers keep records of these data to find weak spots in their network and to determine whether roaming charges apply, among other purposes. Thus, the cell-site data — like mailing addresses, phone numbers, and IP addresses — are information that facilitate personal communications, rather than part of the content of those communications themselves. The government’s collection of business records containing these data therefore is not a search.”
As Carpenter’s appeal to the Supreme Court noted, the existing case law on cell site location information (CSLI) so far is mixed to say the least.
His lawyers noted that “five courts of appeals to consider the Fourth Amendment status of historical CSLI have generated 18 separate majority, concurring, and dissenting opinions, highlighting the need for this Court to act.”
“Without guidance from this Court, a cell phone user cannot know the scope of his constitutional protection, nor can a policeman know the scope of his authority,” the petition added. “As law enforcement seeks ever greater quantities of location data and other sensitive digital records, the need for this Court to speak grows daily more urgent.”
And that quantity is indeed vast. Several groups — including the Electronic Frontier Foundation, the Brennan Center for Justice at NYU School of Law, the Center for Democracy & Technology, the Constitution Project, and the National Coalition to Protect Civil Freedoms — filed an amicus brief in the case last year noting that AT&T and Verizon between them received 126,406 CSLI requests in 2015 and another 61,863 in just the first half of 2016. And for Verizon at least, the groups noted, roughly two-thirds of all requests were warrantless.
Carpenter’s is one of two related cases petitioners have asked the Court to hear. The Supreme Court has not accepted or rejected the other petition, Graham v United States, but whatever decision it returns in the Carpenter case will of course apply broadly to any case where CSLI data is sought.

Editor's Note: This article originally appeared on Consumerist.