Local officials are scrutinizing ShotSpotter gunshot detection system anew: ‘What exactly have we been doing here?’

Somerville City Councilor Willie Burnley Jr. in front of what's said to be a ShotSpotter device attached high on a light pole.Jessica Rinaldi/Globe Staff

SOMERVILLE — For a decade, a network of ShotSpotter sensors has been listening in on Somerville, waiting to hear pops of gunshots. Some of the devices are perched out of view atop buildings. Others blend in, hiding in plain sight on utility poles.

The concept is simple: When the sensors detect telltale bang sounds that could be gunfire, they calculate the coordinates of where the sounds originated, then alert police departments, which can send officers rushing to the scene to investigate.

Supporters say ShotSpotter, which is used in more than 150 municipalities, including Boston and a handful of other Massachusetts cities, saves lives and helps police catch criminals. But for years, civil libertarians have said that the technology is flawed and that it makes it more likely in communities of color that people will have tense or even dangerous run-ins with police, or that they will be accused of crimes they didn’t commit.

Now, amid research suggesting underwhelming results, a data leak that amplified concerns about its use in communities of color, and Chicago’s high-profile decision to stop using it, a debate about the technology is spreading nationally, and officials — including in Somerville — are scrutinizing it with new fervor.

WATCH: Reporter Spencer Buell highlights the civil liberty concerns surrounding ShotSpotter, a sensor that is supposed to pick up the sound of gunshots.

Some elected leaders say they are getting the full picture, for the first time, about how the tech is used, after the release of data that purports to reveal the locations of the sensors, which the ShotSpotter’s parent company has kept secret for years, even from the police and elected officials who approved their installation. Decisions like that of Chicago’s mayor shone a spotlight on a tool that has become so widespread in so many places it became part of the ebb and flow of city life.

Somerville City Councilor Willie Burnley Jr., who called for a hearing to discuss the city’s use of ShotSpotter, said a leaked map of where the devices are supposedly located in his city troubled him.

“It’s concerning to me that these sensors seem to be exclusively in areas predominantly made up of people of color and low-income residents,” he said.

For Burnley, 30, it’s a chance to grapple with what he sees as the unchecked spread of the security state for most of his life, and potentially rein it in.

“I came up in the age of the Patriot Act,” he said. “I worry what we lose when we are unwilling to challenge companies or governments that want to surveil us all the time and do God knows what.”

Secrets, leaked

The increased scrutiny in Massachusetts comes after a February report in Wired magazine, based on leaked internal data, said ShotSpotter devices were used disproportionately in communities of color.

In Boston, where the tech has been scrutinized at City Hall as recently as 2022, councilors called for another hearing.

The ACLU of Massachusetts in a letter last month urged Somerville to abandon the program, citing studies that raise questions about the devices’ efficacy and undercut the pitch of offering a tech-based crime-fighting tool. The letter pointed to a nationwide report from the Journal of Urban Health in 2021 that found from 1999 to 2016, ShotSpotter had “no significant impact on firearm-related homicides or arrest outcomes,” and another from the MacArthur Justice Center at Northwestern that found 89 percent of ShotSpotter alerts in Chicago were “dead-end deployments,” where officers couldn’t find evidence of gun-related incidents. (The company that makes ShotSpotter disputes those findings.)

“How many people have been stopped and shaken down by the gang unit simply because they were a Black or brown kid in the vicinity of a ShotSpotter alert?” said Kade Crockford, director of the Technology for Liberty Program at the ACLU of Massachusetts. “It’s kind of easy to just shrug and say gun violence is a real issue, so we ought to give the police every tool that they need. But now that we have some real evidence about the unreliability, the ineffectiveness, the civil rights harms, and the dangers that can flow from the use of the technology, people are thinking, ‘Wait a second. What exactly have we been doing here?’ ”

‘Based on where crime concentrates’

SoundThinking, the publicly traded company in California that makes the sensors, insists ShotSpotter is accurate 97 percent of the time, a figure that relies on feedback from police and that it said comes from an outside research firm’s audit.

Tom Chittum, its senior vice president of forensic services, said critics don’t account for how challenging it is to substantiate reports of gunfire. He said that if one of ShotSpotter’s alerts doesn’t lead to evidence of a shooting, it’s not because one didn’t occur — it’s because that evidence can be exceedingly hard to find.

As for whether the devices are used disproportionately in minority neighborhoods, Chittum said the company installs them at the direction of police, who consult gun violence data, not demographics.

“It is based on where crime concentrates,” he said.

SoundThinking said police departments tell the company where they want ShotSpotter coverage, but the company keeps the precise locations of the sensors secret. That way, the company says, it can keep criminals from knowing where they are, prevent theft and vandalism, and shield any of the private property owners it partners with from being harassed.

Coming to the state

ShotSpotter arrived in Massachusetts in 2007, when it was deployed in Boston.

“It was a unique technology at the time and we found it helpful,” recalled Ed Davis, who was police commissioner from 2006 to 2013 and now works as a security consultant and counts the Globe among his clients.

There were problems, he said, including that the tech at first had trouble distinguishing between gunshots and backfiring vehicles, often sending officers racing to investigate what turned out to be noisy MBTA bus mufflers.

But, he said, it also helped do things like pinpoint gunshots in Franklin Park, helping police find bullet casings.

Last year, ShotSpotter sent out 627 alerts in Boston, according to data provided by SoundThinking.

“People are concerned about government intrusion, and I totally understand that,” Davis said. “But if you can save a life by getting emergency vehicles to the scene of a shooting faster, then the upside far outweighs the downside in my mind.”

Ed Davis, a former Boston police commissioner, who saw the role of ShotSpotter up close during his tenure.David L. Ryan/Globe Staff

The devices ping less often in Somerville and Cambridge, which began using them in 2014 at no cost due to a federal grant.

In Somerville, ShotSpotter sent out 16 alerts in the 2023 fiscal year, according to police data in a report to the City Council.

Growing suspicion

Somerville elected officials have been critical, and suspicious, of surveillance tech such as cameras, drones, and other tools in recent years. Somerville in 2017 became the first city in the state to adopt rules that require public approval of any new surveillance technology before the police can use it and in 2019 passed one of the country’s first facial recognition bans.

When it comes to ShotSpotter, anyone trying to see the devices in the wilds of Somerville has to look closely.

The Globe obtained a list that a person with knowledge of its contents said revealed the coordinates for the devices in the city. A reporter and photographer, on foot and using Google Maps, laid eyes on a handful of what appeared to be ShotSpotter devices, including one on a light pole in Somerville’s Ten Hills neighborhood, and another on the roof of an apartment complex.

What's said to be a ShotSpotter device is seen attached high on a light pole in Somerville.Jessica Rinaldi/Globe Staff

SoundThinking would not confirm the devices photographed were ShotSpotter sensors, and said it is pursuing legal action against whoever leaked the supposed data.

Somerville Mayor Katjana Ballantyne has not taken a stance on the devices, saying in a statement that she would “carefully evaluate” input at hearings “as we make decisions about the future of this technology in our city.”

Meanwhile, as cities reconsider their relationship with the company, SoundThinking said it would show up at hearings if invited.

“Communities should have input into the tools that their police use,” Chittum said. “I’m glad to see they’re talking about it.”