Many surveillance cameras do capture sound. It's important in investigations to know what was said during an incident.
There are technologies like ShotSpotter - http://www.shotspotter.com/ - which according to the NYT has enough fidelity to pick up things like "doors slamming, birds chirping, cars on the highway, horns honking." as well as conversations:
There are technologies like ShotSpotter - http://www.shotspotter.com/ - which according to the NYT has enough fidelity to pick up things like "doors slamming, birds chirping, cars on the highway, horns honking." as well as conversations:
http://www.nytimes.com/2012/05/29/us/shots-heard-pinpointed-...