July Fourth fireworks or gunfire? How Mpls. cops hear it
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The sound of impromptu neighborhood fireworks displays can be annoying. Things that go bang in the night can be especially disturbing if the noise sounds like gunfire.
Police officials say even trained professionals sometimes struggle to tell the difference between the two kinds of explosions. Was that a gunshot or a very large firecracker?
"That's a roofing nail gun ... No, that sounds to me like gunshots," Minneapolis Police Commander Scott Gerlicher said, correctly, as he listened to several recorded pops, including a bottle rocket, caught by Shotspotter, the Minneapolis gunshot detection system.
Gerlicher says sometimes Shotspotter can immediately differentiate between fireworks and gunfire by comparing the unique sound wave patterns made by both types of explosions. When the system recognizes a gunshot or shots, it notifies the police dispatch center and lets it know where officers should go to investigate.
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Sometimes, the suspected sounds are sent nearly instantaneously to a Shotspotter listening room in California. Gerlicher says analysts make split-second decisions and notify MPD dispatch only if they believe shots have been fired. But they don't always get it right.
"We have had occasions where we never got a notification from Shotspotter that there was a gunfire event. Yet we know that someone was actually shot on a corner," Gerlicher said. "So we've gone back to them and said, 'Hey, check on your system here.' And we've been able to then recover that sound file that was either miscoded, either by the system or the analysts reviewing that audio file."
Company CEO Ralph Clark says the system is 95 to 99 percent accurate, although he acknowledges that might be overstated.
"We are probably missing gun shots that aren't getting reported to us," he said. "That's why we spend a lot of our energy with our customers saying, 'please call us if you ever have a confirmed gunshot that we don't detect."
The fireworks that start up weeks before the Fourth of July make this time of year particularly busy for Shotspotter analysts, said Clark. Cinco de Mayo and New Year's Eve also bring more activations in many of the 85 cities where the company operates, he added.
The Fourth of July holiday weekend is a busy time for police officers, too. Gerlicher wants residents with nuisance complaints about fireworks to call 311. But he adds that if you think you hear gunshots, don't investigate. Call 911.
