US appeals court rules a warrant is required for cell phone location tracking


Big news in the fight for security and privacy in the US: the 11th Circuit Court of Appeals this week ruled that a warrant is required for cell phone location tracking.

Here's the decision PDF, via the ACLU. At Just Security, Jennifer Granick of the EFF writes:

[On Wednesday], the Eleventh Circuit rejected the exceedingly common law enforcement practice of warrantlessly tracking suspects’ physical location using cell phone tower data. The opinion, United States v. Davis, is both welcome and overdue. Defendants who have and will be physically tracked without a warrant have new legal support to challenge that surveillance. Additionally, because the case involved stored cell site data, Davis undermines the government’s legal arguments that other warrantless “metadata” collection practices are constitutional.

Mobile phones leave digital footprints of their owner’s travels through space and time. Whenever these handsets are turned on, even when they are not in use, they send signals to the nearest cell towers so that the communications network system knows where to route a call should one come in. These inevitable “pings” can be used to identify the tower or towers closest to the targeted handset. Since people usually do not share handsets, and since most individuals carry their cell phones with them at all times, tracking pings is a highly effective way of tracking any particular individual’s physical location around the clock.

Not only is cell tracking an effective methodology for determining where an individual suspect or suspects have been or is going, it is also useful for determining the identity of unknown individuals who are near a particular place at a particular time. The wireless provider can identify to law enforcement all the handsets that were connected to any particular tower at any time. This technique is called a “tower dump” and providers charge about $75 for the information, which can disclose the location of any number of individuals. Law enforcement can discover who is or was connected to the towers nearest to a crime or political protest, for example.

How common is cell phone tracking? We don’t have exact numbers, but it is exceedingly common. For example, in 2011, cell phone companies reportedly received over 1.3 million requests for text messages, caller locations and other information.