Something I missed last year: the emeregence of discussion about “geofence warrants.” As reported by The New York Times:

The police told the suspect, Jorge Molina, they had data tracking his phone to the site where a man was shot nine months earlier. They had made the discovery after obtaining a search warrant that required Google to provide information on all devices it recorded near the killing, potentially capturing the whereabouts of anyone in the area.

and

Technology companies have for years responded to court orders for specific users’ information. The new warrants go further, suggesting possible suspects and witnesses in the absence of other clues. Often, Google employees said, the company responds to a single warrant with location information on dozens or hundreds of devices.

Interestingly, there appear to be a series of cases of persons arrested on the back of these warrants now suing the police. An Arizona man is suing for wrongful arrest, and even an alleged robber is suing for privacy violations.