Are gunshot-detecting microphones worth the money?

WALK AROUND one of the poorer neighbourhoods of Chicago and look at the street-lamps. You will see that many of them have protuberances sticking several feet above the light. These are microphones operated by ShotSpotter, a firm with its headquarters in California. They are spread over a large part of Chicago, and they capture the sounds of gunshots. Algorithms pick out the sounds, which are then verified by humans listening in from a control centre in Washington, DC. Triangulating the sounds from several microphones reveals where the guns were fired. Police are alerted and rush to the scene, quicker than if they had to wait for a 911 call—especially one that may not come.