That is the implication of a recent federal appeals court decision that said the government needs a warrant to obtain cellphone location records. While the conclusion is welcome, it can be reconciled with Supreme Court precedents concerning voluntarily disclosed information only by assuming that people do not understand that their cellphones are also tracking devices.
Cellphones have to know where you are in order to work. They are in constant communication with a network of transceivers through the nearest one, and when you make or receive calls, the location of that cell site is part of the information retained by your carrier for billing purposes.
Those records are a trove of personal information because they reveal where you've been throughout the day, every day, for the past year (and possibly longer, depending on your carrier's retention policy). A string of Supreme Court decisions dealing with business records nevertheless suggests that the Fourth Amendment, which bans "unreasonable searches," imposes no restrictions on the government's ability to peruse this information.
That was the conclusion reached by the U.S. Court of Appeals for the 5th Circuit last year. "Cell site data are business records and should be analyzed under that line of Supreme Court precedent," the 5th Circuit said. The Supreme Court repeatedly has held that "a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties."
According to the "third party doctrine," such information has only as much protection as legislators decide to give it. A 2012 investigation by the American Civil Liberties Union found that police often obtain cellphone location data, including real-time tracking as well as records, without a court order of any kind.
Last week the U.S. Court of Appeals for the 11th Circuit ruled that such warrantless surveillance is unconstitutional because "cell site location information is within the subscriber's reasonable expectation of privacy." The case involved a robbery suspect, Quartavious Davis, who was linked to various crime scenes through data obtained from his cellphone company, and the decision hinged on Davis' technological cluelessness.
During Davis' trial, the 11th Circuit noted, a prosecutor conceded that Davis and an accomplice "probably had no idea" they were revealing their whereabouts by using their cellphones. If so, the court said, it hardly seems reasonable to say they voluntarily shared that information.