Your phone constantly tracks and records its location and transmits the information to your wireless carrier. Most phone companies keep that data — known as “cell site location information” — for up to five years. And until last week, it was pretty much available to the government for the asking.
Think for a moment what that means. If you went to a psychiatrist, a divorce lawyer, an AA meeting, a yoga class, or a 1980s dance party in the last five years, any policeman in the country could find out about it just by asking the phone company where your phone was at a given moment in time. It is as though the government placed permanent tracking devices on all of us. True, under federal law, the police had to ask for a court order under the Stored Communications Act based on a showing that the cell site data was “relevant and material to an ongoing investigation.” But that is a ridiculously low standard: pretty much anything an investigator wants to see can be tied to an investigation one way or another. Orders under 18 U.S.C. Section 2703(d) were, in practice, routinely granted by both state and federal courts.
All that changed last Friday when a fractured Supreme Court ruled in Carpenter v. U.S. that grabbing cell site data constitutes a search under the Fourth Amendment. That means that use of cell site data must be reasonable. For police investigations, a search is only reasonable if it is based on a search warrant supported by probable cause. Probable cause, the Court explained, is something more than the low standard in Sec. 2703(d): “relevant and material” just means cell site evidence “might be pertinent to an ongoing investigation,” whereas probable cause requires a “quantum of individualized suspicion” before police can start rummaging. So a Section 2703(d) subpoena is not enough to support obtaining cell site data. Mr. Carpenter’s conviction, based in part on cell site location data showing his phone was near several stores at the time they were robbed, was thrown out.