I saw this on the news a couple of days ago. It's basically a collection of acoustic sensors, deployed in the streets of Boston, that can pinpoint the location of a gun shot through some form of triangulation (that's my educated guess...I am going to try to dig up some info on such a system)
Here's an article on the Globe:
http://www.boston.com/news/local/articles/2006/02/24/keeping_ear_cocked_for_gunshots/
Here's an article on the Globe:
http://www.boston.com/news/local/articles/2006/02/24/keeping_ear_cocked_for_gunshots/