Law enforcement is increasing its use of reverse-location warrants with companies like Google, known as “geofence” warrants. Instead of asking Google, or Verizon, or AT&T for the specific history of a person, these warrants ask for the identifying information of all the people in a certain area. For instance, a bank is robbed, and the authorities file a warrant on Google demanding that all of the Google Maps users with a certain radius of that bank be turned over to authorities. While the perpetrator may be included in that group, it could also potentially include the private data of dozens or even hundreds of innocent people. That’s where the biggest privacy concern arises.
The use of geofence warrants is growing, Google indicated that they were receiving 180 requests per week at the end of last year, and the numbers have been steadily increasing. The cases challenging these searches, generally most will target the lack of specificity and the invasion of privacy, have not yet resulted in many appellate decisions detailing when such warrants may be appropriate. One judge wrote in denying a warrant application, “The potential to use Google’s capabilities to identify a wrongdoer by identifying everyone (or nearly everyone) at the time and place of a crime may be tempting, but if the government can identify that wrongdoer only by sifting through the identities of unknown innocent persons … a federal court in the United States of America should not permit the intrusion.”
There is likely a path to make such reverse-location warrants valid, but it will likely encounter strict scrutiny to ensure limiting the request as narrowly as possible by size, time, and other factors to target the likely offenders, and not invade the privacy of law-abiding citizens. The concerns about unconstitutional intrusions were brought to light when NYC sought geofence data for people protesting and counter-protesting last year in the hunt for data about criminal rioters. The concern here is not only the invasion of privacy, but also the chilling effect on the 1st Amendment rights of lawful protestors. There are a lot of complex issues here, and it will likely be some time for the courts to develop guidance as to when geofence warrants are permissible, and when they are not.