A technician quickly focused on the computer screen, where the words “multiple gunshots” appeared in large type. She listened to a recording of the shots — the tat-tat-tat-tat-tat of five rounds from a small-caliber weapon — and zoomed in on a satellite map to see where the gun had been fired: North 23rd Street in Milwaukee, 2,200 miles away.
At 7:23:48, the technician, satisfied that the sounds were gunshots, sent an alert to the Milwaukee Police Department. Less than two minutes later, or at 9:25:02 p.m. Wisconsin time, a tactical team arrived at the address to find five .22-caliber shell casings and a bleeding 15-year-old boy who had been shot in the arm. The casings, said Chris Blaszak, a detective assigned to the department’s intelligence fusion center, were found within 17 feet of where the alert had placed the gunman. Total elapsed time: 3 minutes, 55 seconds.
Milwaukee is one of an increasing number of cities around the country — just under 70 to date, including some in the New York area — that are using a gunshot detection system called ShotSpotter to pinpoint the location of gunfire seconds after it occurs. Last year, the company that developed ShotSpotter began offering a more affordable system, and that has brought in new clients and led other cities to consider trying it.
The detection system, which triangulates sound picked up by acoustic sensors placed on buildings, utility poles and other structures, is part of a wave of technological advances that is transforming the way police officers do their jobs.
But like other technologies, including license plate scanners, body cameras and GPS trackers, the gunshot-detection system has also inspired debate.
In at least one city, New Bedford, Mass., where sensors recorded a loud street argument that accompanied a fatal shooting in December, the system has raised questions about privacy and the reach of police surveillance, even in the service of reducing gun violence.
And with recession-plagued police departments having to cut personnel and services, some cities have questioned the system’s benefits relative to its cost. The Detroit City Council last year rejected the Police Department’s proposal for a three-year, $2.6 million contract, with one council member objecting that not enough officers were available to respond to the alerts.
Cities that installed ShotSpotter in the past bought the equipment and managed the alerts themselves, a model that often involved laying out hundreds of thousands of dollars. But the company now offers a subscription plan for a yearly fee of $40,000 to $60,000 per square mile that includes round-the-clock monitoring of alerts by trained reviewers here in Mountain View.
Many police officials say the system has significantly improved response time for crimes involving firearms and has increased community confidence and helped deter gun crime by demonstrating that the police can show up quickly at the right place.
The technology, they say, has given officers critical information about what to expect upon arriving at a crime scene — like whether a gun was fired from a car and if so, how fast and in what direction the car was traveling — and has offered a level of precision in locating gunfire rarely afforded by 911 calls.
Sgt. Chris Bolton of the Oakland, Calif., Police Department, which has installed ShotSpotter in high-crime neighborhoods in East and West Oakland, said that before the system was in place, “a patrol officer would receive a gunshot call from the community and you could spend up to 30 minutes driving within, I would say, three to four blocks of that location, just to make sure there isn’t a victim in need of assistance, a crime ongoing or any evidence.”
If nothing else, ShotSpotter has made it clear how much unreported gunfire takes place on city streets. In many high-crime urban neighborhoods, gunshots are a counterpoint to daily life, “as common as the birds chirping,” as Cmdr. Mikail Ali of the San Francisco Police Department put it.
But whether out of apathy, fear or uncertainty, people call the police in only a fraction of cases.