Shot Spotter 
Wired article: "Last year there were 148 homicides in Oakland. Today, when someone fires a gun on a city street, a network of hidden microphones kicks in - triangulating the exact location. And alerting police."
http://www.wired.com/wired/archive/15.04/shotspotter_pr.html

Wired article: "Last year there were 148 homicides in Oakland. Today, when someone fires a gun on a city street, a network of hidden microphones kicks in - triangulating the exact location. And alerting police."
http://www.wired.com/wired/archive/15.04/shotspotter_pr.html