This is a very interesting talk on the ShotSpotter technology by Elecia White and Sarah Newman. This technology has been installed in several major cities, helping to solve crimes when the shooter can be pinpointed quickly. In one example, a sniper shot someone from a roof, and actually stayed on the roof, relaxing and smoking a cigarette - thinking he was out of the expected shooting area. But, the ShotSpotter technology had pinpointed him and the police were able to make an arrest.
Of course, this technology needs to attempt to differentiate between firecrackers, hammers, backfiring cars and gunshots. The technology takes a first pass at guessing what it was hearing (and gives a level of confidence), but then asks the police dispatcher to make a judgment call on whether police action is required or not.
They find this gets faster and better reporting than actually relying on people calling 911 (as there is a longer delay before they call and only about 50% of gun crimes are called in). The system isn't perfect, but seems that it can definitely help!