This covert technology listens for gunshots 24/7 and calls the police on its own A technology known as ShotSpotter is in 90 cities across the US. Skeptics wonder if it's reducing gun violence or just costing cities money.

A technology known as ShotSpotter is in 90 cities across the US. Skeptics wonder if it's reducing gun violence or just costing cities money. This covert technology listens for gunshots 24/7 and calls the police on its own