Gun shot detectors coming to an American city near you

If this really works as advertised, why do we need gun control when we can quickly catch the bad guys who use guns to do bad things? From Fox News:

Gunshots ring out in the dead of night, and not a single person reports it. Yet police know exactly where the shots came from, even before they arrive on the scene.
It sounds like a scene from The Minority Report, but it's real. A new technology called ShotSpotter enables law enforcement officials to precisely and instantaneously locate shooters, and it has been quietly rolling out across America. From Long Island, N.Y., to San Francisco, Calif., more than 60 cities in the U.S. have been leveraging ShotSpotter to make their streets safer. . . .
“If You Fire a Gun, We Will Find You.”
ShotSpotter relies on wide-area acoustic surveillance and GPS technology to triangulate the source of gunshots. Sensors are fixed to buildings and poles to provide coverage over a fixed area. With audio-analysis software, it can identify whether a shooter is stationary or moving -- meaning police officers can be equipped with information on the speed and direction of, say, a vehicle from which a shot was fired.
It can also “hear” the acoustic signature and distinguish between calibers and types of firearms. Similarly, it can hear different explosions and classify them, from vehicle backfires to fireworks to bombs.
The ShotSpotter Gunfire Alert system then relays the location and data to the police or a dispatch computer within moments, enabling a more rapid response time for both police and first responders.
The best part: ShotSpotter works. It's accurate to 10 to 15 feet, and some police departments are reporting accuracy to within five feet. In Long Island’s Nassau County, gun violence was reduced by a whopping 90 percent at the close of this year’s first quarter. . . .
The subscription-based implementation called ShotSpotter Flex costs as much as $60,000 per square mile. . . .