From city streets to the savanna, high-tech system listens for gunshots

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ShotSpotter is based on networks of acoustic sensors that are installed across the subscribing towns. The sensors and their associated electronics are housed in small, unassuming metal boxes that don't look out of place mounted on utility poles or on the side of buildings.

The operators here have listened to thousands of such recordings and, to her trained ears, the sound -- more of a pop than the roaring bang we're used to hearing in movies. "When a gun is fired, the sound from that gun radiates out ... and reaches each one of those sensors at a slightly different time," he said.

The time differences are used to triangulate the location where the sound occurred. It takes about 10 seconds for the triangulation to take place, after a computer algorithm has helped to dismiss things like echoes from nearby buildings.

The use of ShotSpotter is now being expanded beyond gritty urban streets into a completely new environment: the savannas of South Africa. SST has started a trial of its system to detect gunshots from poachers, Beldock said.

The sound of a gunshot travels about twice as far in a savanna or even a jungle as it does in a town, so the density of sensors can be reduced. It's too early to gauge the success of that project, but the hope is that it will serve as a deterrent to poachers or help catch them.