This is a very interesting article about police surveillance and how one of these programs works. Lots of potential here for stopping crime. What do you think, invasion of privacy or not?
https://www.bloomberg.com/features/2016-baltimore-secret-surveillance/
http://arstechnica.com/tech-policy/2016/08/to-find-suspect-city-cops-ran-stingray-for-hours-then-called-in-fbi/
https://www.theguardian.com/us-news/2016/aug/26/stingray-oakland-police-fbi-surveillance