The brief argues that cell-phone location data "reveals a detailed map of a person's location over time," and urge the court to take seriously the US Supreme Court's admonishment in Kyollo to reject "mechanical interpretations" of the Fourth Amendment, and the 7th Court of Appeals declaration that "The meaning of a Fourth Amendment search must change to keep pace with the march of science."
There are now more cell phones than people in the United States, according to the brief, and 56% of them are "smart phones" that allow for even more accurate location tracking (because they're constantly pinging the nearest cell tower for emails, texts, etc..) The growth in smart phone use has been accompanied by an explosion in the number of cell towers, which as a practical matter "means that a person's location can be pinpointed with even greater precision." EFF cited a 6th Circuit case, US v. Skinner, in which:
law enforcement was able to track a phone (and the person carrying it) almost 770 miles from Tucson, Arizona to Abilene, Texas over two days. Agents could see the suspect's travel point by point, and waited until he stopped at a rest stop before swooping in to arrest him. Most critically, [a]t no point did agents follow the vehicle or conduct any type of visual surveillance." The cell phone made the government surveillance easier. Agents would not need to follow the truck physically around the clock or run the risk that they would be discovered. Nor did they need to find a way to surreptitiously install a GPS device onto the truck to track its movements. Instead, as the New Jersey Supreme Court recently noted, cell site information "is akin to using a tracking device that can function as a substitute for 24/7 surveillance without police having to confront the limits of their resources. (Citations ommitted.)Further, "cell phone tracking can even reveal information about a person in the most constitutionally protected space: a home. One federal magistrate judge has noted 'pinging a particular cellular telephone will in many instances place the user within a home, or even a particular room of a home.'"
Argued the brief, "Imposing a search warrant requirement would not result in an unnecessary burden on law enforcement because the law currently requires the government seek judicial authorization before obtaining" cell-phone location data. Under Texas law, by comparison, the current standard for obtaining this information is less clear. In legislative hearings last spring, most agencies said they too were seeking court orders - albeit at a lower standard than required for a warrant - to access cell-phone location data. But the Texas Department of Insurance told legislators it obtained that information using only a subpoena, and representatives of cell-service providers said they provided information under both subpoenas and court orders based on reasonable suspicion. The EFF brief concluded:
cell-phone location data "is a valuable crime fighting tool because of its power to intrude on a traditionally private sphere to obtain an enormous amount of sensitive information about where a person has been, their patterns of movements and their associations and affiliations. Law enforcement should be permitted to use this information to keep people safe, provided they adhere to strict safeguards designed to protect privacy. The proper way to balance these interests is to require a search warrant supported by probable cause before authorizing disclosure of cell site location information.Expect similar arguments to be made next year when the Texas Lege again considers these issues. Maine, Montana and New Jersey have all instituted warrant requirements for police to access this information and I fully expect other states to follow suit before the 84th Texas Legislature re-convenes. Indeed, if the scandal over the NSA's collection of cell-phone records had erupted just a couple of months earlier than it did, I have little doubt Texas would already have passed such legislation. If we get it done in 2015, though, that would still be better late than never.