A document obtained by BuzzFeed News shows the US Department of Homeland Security used secretive cell phone–tracking devices nationwide more than 1,800 times from 2013 to 2017.

The information, obtained through a Freedom of Information Act request, shows that Homeland Security Investigations, a major investigative arm of DHS, used what‘s known as cell-site simulator over-the-air technology 1,885 times from Jan. 1, 2013, to Oct. 11, 2017 throughout the US.