(20.11.2009) The ShotSpotter system uses microphones that transmit the sound of a gunshot to a police mainframe computer seconds after the firing. The wireless sensors also gauge their distance from the noise, like bats, triangulating the information to direct the police to the shooting site. If the system sounds like Big Brother, it is, kind of — except, one police official insisted, it eavesdrops only on things that go bang.