A state court in Florida just ruled that police need a search warrant to access cell phone tower data:
Americans may have a Florida drug dealer to thank for expanding our right to privacy.

Police departments around the country have been collecting phone metadata from telecoms and using a sophisticated spy tool to track people through their mobile phones—often without obtaining a warrant. But a new ruling out of Florida has curbed the activity in that state, on constitutional grounds. It raises hope among civil liberties advocates that other jurisdictions around the country may follow suit.

The Florida Supreme Court ruled Thursday that obtaining cell phone location data to track a person’s location or movement in real time constitutes a Fourth Amendment search and therefore requires a court-ordered warrant.

The case specifically involves cell tower data for a convicted drug dealer that police obtained from a telecom without a warrant. But the way the ruling is written (.pdf), it would also cover the use of so-called “stingrays”—sophisticated technology law enforcement agencies use to locate and track people in the field without assistance from telecoms. Agencies around the country, including in Florida, have been using the technology to track suspects—sometimes without obtaining a court order, other times deliberately deceiving judges and defendants about their use of the devices to track suspects, telling judges the information came from “confidential” sources rather than disclose their use of stingrays. The new ruling would require them to obtain a warrant or stop using the devices.

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The Justice Department has long asserted that law enforcement agencies don’t need a probable-cause warrant to use stingrays because they don’t collect the content of phone calls and text messages. Instead, authorities say, they operate like pen-register and trap-and-trace systems, collecting the equivalent of header information. A pen register system records the phone numbers that a person dials, while a trap-and-trace system records the phone numbers of incoming calls to that phone.

This is going to be appealed to the Federal Courts, and it will end up at the Supreme Court, where, unless Antonin Scalia chokes on his own bile in the interim, I expect a 5-4 decision saying that no warrant is needed.