Tested and working in Flint and Saginaw, and used in prosecutions.

http://www.mlive.com/news/saginaw/in...aim_to_re.html

High-tech microphones aim to record, report gunshots in Saginaw

...ShotSpotter is a specialized sonar device, triangulating the time and origin of gunshot-like sounds using 15 to 20 microphones on structures or telephone poles within a one-mile radius. The devices alert authorities "within a matter of seconds" via computer, using global positioning system navigation to point the way.
The microphones can determine the direction and speed of shooters on the move. The system can differentiate between a shotgun blast, a pistol discharge, fireworks or a car backfiring.
ShotSpotter is mobile, too. While it only covers one mile at a time, police can move the microphones as crime "hot spots" shift in the city.
"As we solve problems in one area, we can move it to another," Cliff said...
You can read more about the system at the link above. So far, it has supposedly been working beautifully, according to the local media. The microphones are hidden, and never allowed to be photographed, to prevent vandalism and criminals "shooting them out" the way they currently do to video equipment.

Keeping in mind that Saginaw has ranked right up with Detroit in gun violence;

A safer Saginaw? City records one homicide through first four months of 2010

SAGINAW — For the first four months of this year, and despite Saginaw’s violent reputation, gun violence has fallen by 61 percent over the same period five years ago.

The city has recorded only one homicide from January to April. In April, one person was struck by gunfire. The lack of violent crimes has Saginaw police officials hopeful that the trend will continue through the traditionally violent summer months...

...n the first four months of 2006, officers responded to 44 shootings — including nine that were fatal. By the start of May 2010, the number of shootings had dropped to 17, with one fatality.
While the technology is being hailed as a success, it is of course just another great tool for officers. Improved technology went hand in hand with tough decisions not to cut police officers.