If police want to track your movements using old calls you made on your cellphone, they can get the information from your cellphone company without a warrant. They just need to show a court it will help in a criminal investigation. That’s the upshot of a ruling yesterday in the Fifth Circuit Court of Appeals.

The ruling relies on the U.S. Constitution’s Fourth Amendment, says says the ACLU’s Nathan Freed Wessler.

According to Wessler, the court ruled that: “Historical cellphone location information about a person is a business record of the phone company, that cellphone users voluntarily share with that company, and therefore those users have somehow given up their privacy interest in their location data.”

The court said consumers understand calls have to be connected through a cellphone tower, and that information can be tracked by the company.

“That presupposes that people actually understand the technical architecture of a cellphone network every time they make a call,” Wessler says.

The court also said this is explained in a customer’s terms of service.

“Those are huge legal documents,” says Carl Howe of the Yankee Group. “They’re mostly incomprehensible to the average consumer. I think expecting that constitutes disclosure is optimistic at best.”

Federal courts in Virginia and Georgia have pending cases that may yet extend more privacy to cellphone calls.