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90 Cities Install A Covert Technology That Listens For Gunshots (businessinsider.com)
An anonymous reader quotes Business Insider:
In more than 90 cities across the US, including New York, microphones placed strategically around high-crime areas pick up the sounds of gunfire and alert police to the shooting's location via dots on a city map... ShotSpotter also sends alerts to apps on cops' phones. "We've gone to the dot and found the casings 11 feet from where the dot was, according to the GPS coordinates," Capt. David Salazar of the Milwaukee Police Dept. told Business Insider. "So it's incredibly helpful. We've saved a lot of people's lives."
When three microphones pick up a gunshot, ShotSpotter figures out where the sound comes from. Human analysts in the Newark, California, headquarters confirm the noise came from a gun (not a firecracker or some other source). The police can then locate the gunshot on a map and investigate the scene. The whole process happens "much faster" than dialing 911, Salazar said, though he wouldn't disclose the exact time.
The company's CEO argues their technology deters crime by demonstrating to bad neighborhoods that police will respond quickly to gunshots. (Although last year Forbes discovered that in 30% to 70% of cases, "police found no evidence of a gunshot when they arrived.") And in a neighborhood where ShotSpotter is installed, one 60-year-old man is already complaining, "I don't like Big Brother being in all my business."
When three microphones pick up a gunshot, ShotSpotter figures out where the sound comes from. Human analysts in the Newark, California, headquarters confirm the noise came from a gun (not a firecracker or some other source). The police can then locate the gunshot on a map and investigate the scene. The whole process happens "much faster" than dialing 911, Salazar said, though he wouldn't disclose the exact time.
The company's CEO argues their technology deters crime by demonstrating to bad neighborhoods that police will respond quickly to gunshots. (Although last year Forbes discovered that in 30% to 70% of cases, "police found no evidence of a gunshot when they arrived.") And in a neighborhood where ShotSpotter is installed, one 60-year-old man is already complaining, "I don't like Big Brother being in all my business."
ShotSpotter has had this for over 20 years in cities. In some tinfoil hat just learning about it?
San Francisco Bay Area police departments have been using this technology for years.
ShotSpotter has been used for several years in six Bay Area cities. Police say ShotSpotter has helped them respond more quickly to crime scenes and capture suspects, and provide court evidence to solve homicide cases. Oakland police started using the gunshot detection technology in 2006; it now covers 80 percent of the city, said Capt. Ersie Joyner.
http://www.mercurynews.com/2013/11/11/shotspotter-has-long-history-with-bay-area-police/
It's probably less expensive to move a sensor that listens for gunshots than an entire police precinct. It also doesn't really matter where you locate the precinct either since the police can take their cars and patrol wherever they're most needed. You'd want to have your precincts located in such a way that it makes it easy and efficient for police to deploy anywhere in the city, otherwise if you locate them nearest the worst neighborhoods you'll probably not have a very even distribution as bad neighborhoods tend to be clustered.
Not really. Unless you really have a barrel length of zero and a round of zero mass, there will be a sonic boom from the bullet for at least a little while. A microphone staged downrange will pick up two cracks: one from the sonic boom of the bullet and a second one from the charge exploding. The bullet is supersonic, so the sound from it originates closer to the microphone, whereas the gun is stationary and its sound will arrive later. The reverse is true if the microphone is behind the gun, and there's an area of ambiguity if you're perpendicular to the muzzle on either side, which is why multiple microphones.
Firecrackers, nail guns, and anything else that doesn't send a supersonic projectile doesn't have that double crack. It's not hard to tell by ear in many cases and certainly not too hard to automate classification to some acceptable level of false alarm rates.
Slight nitpick, sub-sonic .22LR rounds are a thing.
"So long and thanks for all the fish."
Shannon's Law was directed specifically at celebratory gunfire, such as firing into the air for New Year. This is a feature of, um, a certain culture. Shannon was a young girl who went outside with her family to see the New Year in and suddenly dropped dead of a round that had been fired miles away.