Geofencing is often used by marketers to target customers in a specific geographic location, for example to send coupons to potential buyers who are within a specified range of a retail store or restaurant. It has also been used by political campaigns to identify people who have attended rallies or who attend church or group meetings that may suggest their political leanings. Now police are using geofencing to determine who may have been in the vicinity when a crime was committed.
A geofence warrant is the opposite of a typical search warrant. Normally, police identify a suspect and receive a warrant to search the person’s home or property after showing probable cause. With a geofence warrant, police start with the time and location of the crime then request data from one or more tech companies about devices (such as mobile phones) that were in the area. Police investigate an anonymous list and then may request more specific data about devices of interest.
Geofence warrants are often sent to Google because they have the most far-reaching data gathering systems. Although Google collects the information in their Sensorvault database for advertising purposes, police are turning to the data for help in their investigations. In a December 2019 court document, Google said the data provided by the Sensorvault database is often more accurate than phone tower location logs alone because its location data comes from a combination of GPS signals, Wi-Fi networks, Bluetooth beacons and cell tower data.
But Google is not the only place gathering location data. Location data is collected in a myriad of ways, including from companies such as Apple, Lyft and Uber, or from apps for weather, games and other services.
Critics of using geofencing in this manner say it is an invasion of privacy that gathers data about the guilty and the innocent alike. In one case, an Arizona man was arrested on suspicion of murder based on evidence from a geofence warrant. During the week he spent in jail before being exonerated he lost his job and his car.
It is also possible to bypass getting a warrant and buy geofencing data from marketers who have captured the information that is needed. A bill introduced in New York state would prohibit the purchase of geofencing location data from a data broker as well as banning reverse search warrants. There is currently no federal law regulating these search warrants.
While the legislatures and the courts work out the constitutionality of using this data in criminal cases, there are steps you can take to reduce your footprint. After all, you do not need to be a criminal to get caught up in an investigation based on location data.
According to Google, data is only collected in Sensorvault when location history is enabled. Mark Rumold of the Electronic Frontier Foundation says, “Make that feature as useless as possible [by turning off location history], and these warrants will stop.”
