Timothy Carpenter, was convicted of robbery in Detroit, based in part on months’ worth of phone location records the government obtained without a probable cause warrant. The records covered 127 days, revealing 12, 898 separate points of location data.
Carpenter's attorneys from the ACLU argue that cell phone location data reveals a lot about a person.
"A person who knows all of another's travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups -- and not just one such fact about a person, but all such facts," the appeal says
In 1979, in Smith v. Maryland, the Supreme Court ruled that a robbery suspect had no reasonable expectation that his right to privacy extended to the numbers dialed from his phone. The court reasoned that the suspect had voluntarily turned over that information to a third party: the phone company.
Relying on the Smith decision’s “third-party doctrine,” federal appeals courts have said that government investigators seeking data from cellphone companies showing users’ movements do not require a warrant.
The Supreme Court has previously limited the government’s ability to use GPS devices to track suspects’ movements, and it has required a warrant to search cellphones.