The US Court of Appeals for the Fifth Circuit has ruled that historical cellphone location data is not protected by the Fourth Amendment, allowing police to access the data without a search warrant. The court, whose decisions apply in Texas, Louisiana, and Mississippi, says that such the information is "clearly a business record" that belongs to carriers, noting that "the government does not require a member of the public to own or carry a phone... the government merely comes in after the fact and asks a provider to turn over records the provider has already created." The decision adds to a growing number of federal cases that have split sharply on the issue of warrantless tracking: last year the Sixth Circuit ruled that police do not need a warrant to track phones using GPS, while the Third Circuit ruled in 2010 that warrants are indeed required.

"The government does not require a member of the public to own or carry a phone."

The Fifth Circuit ruling acknowledges that "cell phone users may reasonably want their location information to remain private," but notes that the solution is for people to "lobby elected representatives" to instigate legislation to protect their data, or demand that carriers stop storing the records in the first place. Unless that happens (or the Supreme Court overturns this decision), police in the Fifth Circuit will be able to access cellphone location data with only a court order, rather than a narrower (and harder to obtain) search warrant.

The court's decision is notable in that it characterizes location data as a "business record," which means that the phone companies own the data and can be required to turn it over directly, the same as any other transaction record. Previous cases have focused on an individual's reasonable expectation of privacy, finding that the expectation is lessened when sharing information with a third parties like internet service providers and phone companies. Those decisions have been sharply criticized — by defining cellular location data as a business record, the court's decision steps around that thorny issue entirely.

It's worth noting that the court is referring to specific requests for data — asking for the location data of a single cellphone is okay, while asking for all the data from a particular area at a particular time isn't. That said, advocacy groups, such as the American Civil Liberties Union (ACLU), aren't happy with the ruling. "There is no cell phone company that doesn't retain historical cell site location data," says Catherine Crump, ACLU Staff Attorney. "Our Fourth Amendment rights should not depend on the largesse of for-profit corporations... the mere fact that some other branch of government could provide a remedy is no reason for the courts to take a pass on protecting Americans' privacy."

With a clear split in the circuits over both the legality of warrantless cellphone tracking and how that tracking might be justified, the next step is for the Supreme Court to field a further appeal and issue a nationally-applicable decision. The court held last year that police need a warrant to affix a GPS tracker to a suspect's car; that decision was hailed as a victory for privacy advocates but the court did not address whether similar tracking done by phones would also require a warrant.

Additional reporting by Nilay Patel

Read next: Top 10 things to be afraid of from Black Hat and Def Con