As The New York Times reported this weekend, a series of freedom‐​of‐​information requests by the American Civil Liberties Union have confirmed what privacy and surveillance wonks long suspected: The use of cell phones as tracking devices by state and local law enforcement has become extremely common over the past few years, and is often done without the check of a Fourth Amendment search warrant based on probable cause.





More than 200 law enforcement agencies have responded to the ACLU’s request so far, and all but ten acknowledge tracking cell phone location for some purposes. Many do so primarily in emergency situations to locate potential victims of crime or accident, and of those that also make use of location tracking for investigative purpose, several insist that they always obtain a probable cause warrant. But many others either have unclear standards, or rely on subpoenas or court orders based on the low and easily‐​met standard of “relevance” to an investigation. In effect, they assert the right to put a virtual tracker on citizens—the same conduct the Supreme Court unanimously held to be covered by the Fourth Amendment when a physical tracking device is used—without any need to persuade a judge that a lojacked individual is actually engaged in any criminal conduct.





Perhaps the most troubling revelation, however, is the evidence that at least a handful of law enforcement agencies reported seeking “tower dumps” revealing everyone near a location at a particular time, a form of mass surveillance that can be used to generate a list of potential suspects. I was aware of only one previous case where such a method had been used, back in 2008 in Texas, and at the time that case was unique as far as anyone knew. Now, however, it appears to be sufficiently routine that major providers have a standard price sheet: A one hour “tower dump” from T‐​Mobile will run you $150, while Verizon Wireless charges $30–$60 for every 15‐​minutes worth of mass location data. This is a method in serious tension with our constitutional tradition of “particularity” in searches, and if it were to be permitted under any circumstances, it would require extraordinary safeguards, ideally established by a clear legislative framework—not a patchwork of agencies making up the rules as they go.





Don’t be surprised if you hadn’t heard about this happening in your town: Training materials obtained by the ACLU instruct police to never mention such tracking capabilities when speaking to media, and to omit them as far as possible from police reports. The goal, no doubt, is to avoid reminding criminals that any powered‐​on phone is a potential tracker. But this also means that a signally intrusive form of government monitoring has become widespread with minimal public awareness, let alone discussion or debate. Let’s hope media attention to these disclosures changes that.