At Issue: How Gunshot Detection Prevents Future Crime

Rocky Mount, N.C., a city of about 60,000 people, has used a gunshot detection system to thwart planned criminal acts.

by / November 7, 2011
Rocky Mount, N.C., a city of about 60,000 people, has used a gunshot detection system to thwart planned criminal acts. Photo courtesy "Cast a Line" / Flickr CC Flickr Creative Commons

One morning in the middle of the week in Rocky Mount, N.C., a single gunshot rang out — at least it could have been a gunshot. It also could have been a vehicle backfire or someone setting off a leftover firecracker from the Fourth of July. No one in Rocky Mount called the police, which isn’t unusual: In most cities, only about 20 percent of gunshots are reported.

Rocky Mount officials didn’t need someone to call in. According to Police Sergeant Kevin Bern, the sound was picked up by the city's ShotSpotter gunshot detection system, relayed instantly to a call center in Pasadena, Calif., where acoustics experts looked at the wave form and determined it was, indeed, a gunshot. Seconds later, the location and contextual data came back to the Rocky Mount Police Department.

"We're looking at it from here," said Bern, "and directing the sergeant on the scene to go to the right-front corner of a duplex. She did and found the shell casing." What followed, said Bern, was a "knock and talk" to gather information. "We found out there were a bunch of felons in the house with five stolen guns. Three of them were stolen from addresses in Rocky Mount." Arrests were made, stolen guns were recovered and burglary cases were cleared — all from one gunshot.

According to Bern, when guns are stolen and are about to be sold, thieves will fire them to make sure they work. Or random gunshots can indicate preparation for gang violence. These "confidence" shots – if detected and located -- can alert police in time to prevent crimes in the future.

In one such case, said Bern, gang members were firing off weapons in preparation for a drive-by shooting that night, not realizing the shot detection system had them in its crosshairs. "So who knows how much crime that prevented? There might have been retaliation that night, innocent people could have been hit as well," Bern said.

Berne is enthusiastic about the gunshot detection system and its contributions to the safety of officers and the public. A Rocky Mount ordinance prohibits discharging a firearm in the city, but even so celebratory holiday gunfire sends bullets into the air, and they always come back down. "Or someone steps out their back door in the middle of the night and shoots their gun because they've had a few too many drinks," said Bern. Once the public knows police can locate gunfire, he said, these "celebrations" dwindle.

Rocky Mount’s detection system determines if a shooter is moving or stationary, and data from a drive-by shooting, for example, returns vehicle speed and direction. "So officers are able to stage up when going there, knowing the car is going a certain direction," said Bern. The police department has successfully intercepted several such vehicles, recovered handguns and made arrests.

Locational accuracy is better than expected, said Bern. The system’s maker claims accuracy to 10 and 15 feet, he said, “but we're finding it's getting us to within five feet of where the shell casings are."

One unexpected benefit, said Bern, is the system is very useful for crime analysis.  "You can go back a week or two — or 90 days — and look at patterns, and they start showing up. It's pretty apparent which houses you're having a problem with. There's a cluster of dots around specific houses and you know that's probably a house where some bad guys live. People are shooting at the house, or they're shooting from the house at people. So it could be a drug house, or anything. It works really well for getting a good visual for crimes going on in your city. And there are some tools for that built into the software."


Since gunshot detection systems appeared back in the 1990s, the technology has improved substantially, and false positives -- a complaint of early adopters -- have been reduced if not yet eliminated. Cost has been an issue. Last year Rocky Mount used a $350,000 Department of Justice Grant to purchase coverage for one square mile of the city. Now a subscription-based model has enabled the city to triple its coverage without increasing the cost. "It's a better situation for us," he explained. "With this subscription-based model, they own the equipment; we don't have to worry about maintaining it, paying for damage, etc."

The city is looking for more funding to expand the system further, but probably won't install video cameras. "We'd love to have cameras," said Bern. "Avrio RMS is a partner company, and I've talked to them. The cameras are great, they spin around toward the direction of the shot, but of course that's another cost, so we're really focusing on expanding what we have now."

Wayne Hanson

Wayne E. Hanson served as a writer and editor with e.Republic from 1989 to 2013, having worked for several business units including Government Technology magazine, the Center for Digital Government, Governing, and Digital Communities. Hanson was a juror from 1999 to 2004 with the Stockholm Challenge and Global Junior Challenge competitions in information technology and education.