Reverse warrants are the new regular warrants. Ever since law enforcement discovered most Americans carry tracking devices with them 24/7, they've been approaching cellphone providers with warrants targeting geographic areas rather than people.

When a crime has been committed but cops don't have any suspects, they ask Google and others to canvass the area for them. Officers hand providers a geofence and ask for everyone who wandered into the selected area during a certain timeframe. Once cops have everyone, they start looking for someone.