2018 |by Rachel Levinson-Waldman | BRENNAN CENTER FOR JUSTICE at New York University School of Law |
How is cell phone location data collected?
A cell phone’s location information can be collected in several ways. First, a cell phone accesses its network through signals transmitted by cell towers.7 The cell phone searches for the strongest signal and continually connects to a cell tower as the user moves within the network, whether or not a call is underway.8 When it connects to a cell tower, the phone transmits identifying information to the service provider.9 This enables the provider to “track the phone, discontinue service, or blacklist it from a network.”10 The density and proliferation of cell towers make it increasingly possible to locate an individual phone to within a few feet of its position.11
Service providers collect and store this location data, called cell site location information (CSLI), at least temporarily; some providers keep the data for up to seven years.12 Police officers can obtain stored CSLI if they satisfy certain legal requirements. Prior to 2018, law enforcement agents generally obtained CSLI with a court order under the Stored Communications Act, which has a lower standard than a warrant.13 However, the Supreme Court recently held in U.S. v. Carpenter (2018) that the police must get a warrant to obtain seven days or more of CSLI.14 Police may also request information about every device connected to a single tower during a particular interval, potentially netting historical lo- cation information from thousands of phones; this technique is colloquially known as a “cell tower dump.”15 For instance, in 2010, the FBI received over 150,000 numbers in a single dump in an effort to determine if a suspect had been near several banks that had been robbed.16 Verizon had more than 14,000 cell tower dump requests in both 2016 and 2017 and is on track for even more in 2018.17