Boston police on patrol earlier this month say they heard “several loud bangs,” confirmed by a gunfire locator service called ShotSpotter, leading them to arrests of a Roxbury man on firearm charges.

In New Bedford, a local man was detained last year after the system alerted police to a shooting near a housing development.

And in Worcester, police say information from the technology led them to arrest a 26-year-old in December for a series of gun and drug charges.

Law enforcement tout the arrests as examples of the benefits of controversial technology that detects gunshots and alerts police about their location. Over a dozen communities in Massachusetts use the technology that many in law enforcement, and the company itself, insist saves lives.

The technology company said its customers in the state are Boston, Cambridge, Somerville, Chelsea, Everett, Revere, Pittsfield, Worcester, Lawrence, Brockton, New Bedford, Holyoke, Springfield and Northeastern University. GBH News reached out to all departments and the school for comment on their usage. Only Cambridge and Springfield replied.

A growing number of critics — including some public officials in Boston and Somerville — worry about the effectiveness and reliability of the technology as a public safety tool, saying it discriminates against communities of color and contributes to over policing.

Boston-based attorney Connie Tran says one of her clients was arrested and detained in the summer of 2022 after gunshots were detected in Cambridge. No firearm was found, and there were no witnesses to a shooting. She says his story exemplifies how the technology can erroneously put people behind bars.

“ShotSpotter is central to the government’s ability to prove the gun charges,” Tran told GBH recently. “The government is going to ask the jury to determine a person’s guilt or innocence based on ShotSpotter technology, because there is no gun to test.”

Why ShotSpotter?

The California-based technology company, whose parent company recently changed its name to SoundThinking, launched in 1996. They say its technology is used by police in more than 160 cities nationwide.

Where it’s used in Massachusetts

  • Boston
  • Brockton
  • Cambridge
  • Chelsea
  • Everett
  • Holyoke
  • Lawrence
  • New Bedford
  • Northeastern University
  • Pittsfield
  • Revere
  • Somerville
  • Springfield
  • Worcester

Source: SoundThinking, in an email to GBH News

Tom Chittum, SoundThinking’s senior vice president of Analytics and Forensic Services, told GBH News that ShotSpotter is part of a “comprehensive approach to addressing gun violence.” It is a public service, he says, that can create a country where everyone feels safe to sit on their “front porches.”

At its core, the technology is a microphone and sensor that detect loud sounds that may be gunfire. Recordings are then transmitted to human examiners for forensic analysis. If sounds are suspected to be gunfire, the company alerts local police.

Once police departments contract with the company, they send historical data on where gun crimes have occurred, and establish a desired “coverage area.” SoundThinking places audio sensors in clusters, but doesn’t tell police departments specifically where. These microphones are discreetly hidden, such as on buildings or even atop billboards, according to a WIRED analysis of leaked data.

Chittum said that there’s a chronic underreporting of gunfire by people who are “resigning themselves” to living with that sound in their communities. He said claims that the technology focuses on demographics when deciding where to set up sensors is “baseless.”

“Whatever the reason, we know a substantial number of these shootings [nationally], go unreported as much as 80%. That means four out of five opportunities are missed by police to respond,” he said.

Supporters of ShotSpotter

Springfield has used the technology for over a decade. Ryan Walsh, a police department public information officer, said there are between 80 to 100 shooting victims in Springfield each year. He said 70% of the times officers respond to a ShotSpotter alert and find evidence at the scene, the department hadn’t received a 911 call about the incident.

He said the technology helps increase officers’ response times to shots fired — saving as many as 10 to 15 lives a year.

“The amount of time that they’re [victims] out on the street, not getting the first aid that they need, or getting to the hospital,” he said. “It’s really about the victims for us.”

Holyoke started using ShotSpotter in 2023 because they weren’t getting 911 calls from locals about gunfire.

“I think the sheer number of ShotSpotter activations we’re seeing ... has kinda been eye opening,” Jay Parnell, a detective with the department, said in a department video shared on Facebook last fall.

Holyoke and Springfield are just two of 13 Massachusetts municipalities that have the technology.

A map of ShotSpotter activations published by the City of Holyoke on a monthly basis.

Boston has a three-year, $782,000 contract with SoundThinking that expires in June. In a recent budget hearing related to the Boston Police Department, councilors raised concerns of racial profiling in the areas the sensors are placed in the city, information that was recently included in WIRED’s article.

Boston City Councilor Henry Santana, chair of the Public Safety and Criminal Justice committee, said he is planning to hold a hearing on the matter. City Council President Ruthzee Louijeune told GBH News it’s important for the council to review the technology and consider whether the benefits of ShotSpotter outweigh any potential harm.

“Those are the questions that we need [to answer],” she said. “You know that in my purview as the city councilor at large, representing every neighborhood and city council president, making sure that, you know, police officers work for us.”

But Boston Police Commissioner Michael Cox declined to hold off on signing a new SoundThinking contract.

“We’re not willing to delay a tool that will save lives in the city that we currently use,” Cox said. “The fact is that the faster we respond to something, particularly if a person is shot, the faster they can get help, and the more they survive.”

Cambridge police officials also say ShotSpotter has helped law enforcement gather information about gunfire incidents that have led to increased prosecutions.

“It helps expedite our response in the event that there are gunshot incidents, which can result in potentially saving lives, increasing weapon-related arrests, and ultimately enhancing the safety of our neighborhoods,” a spokesman said.

Critics of the technology

Recently, several Massachusetts lawmakers wrote a letter to the Department of Homeland Security seeking an investigation into the technology. They say they worry it violates the Civil Rights Act, which bars groups receiving federal money from discriminating on the basis of race.

An analysis by the American Civil Liberties Union of Massachusetts’ of more than 1,300 Boston police reports found nearly 70% of ShotSpotter alerts yielded no evidence of shots fired. Using Boston Police Department records, the ACLU said sensors in Boston are primarily installed in Dorchester and Roxbury, neighborhoods that are overwhelmingly Black and Latino.

Kade Crockford, director of the Technology for Liberty Program at the ACLU of Mass, said the city of Boston should wait to sign a new contract until the city council discusses the nonprofit’s findings.

Crockford said in one case, the police pulled someone over in the area because it looked like the tint on their window was too dark and discovered the person was driving without registration, towed the car, and issued a summons.

“It’s that kind of thing that concerns us that police are using ShotSpotter alerts as justification to stop and potentially even search for, arrest Black and brown members of our community, who are just going about their business, going to work, going to school, going to pick their kids up, going to pick up food,” Crockford said.

SoundThinking told GBH News that it has read the letter requesting a Department of Homeland Security review of their practices, but that the company had not “drilled down into every claim.”

“On the surface, we believe this letter and its claims are without merit and we are confident that the DHS will see through this baseless attempt to disparage this critical public safety technology. ShotSpotter saves lives in the places hit hardest by gun violence,” the company said in a statement.

Eric Piza is a professor of criminology and criminal justice at Northeastern University who recently led a study into 15 years of ShotSpotter data and crime calls from Chicago and Kansas City, Missouri. He said that on the one hand, the technology “seems to do what the vendor promises” — SpotSpotter alerts come in about 93 seconds before the first 911 call. Ballistic evidence is collected more often at ShotSpotter scenes than other shootings. But Piza said that researchers didn’t find that those benefits translated into meaningful improvement in public safety.

“Gun violence was no more likely to go down following the introduction of ShotSpotter, and [both fatal and nonfatal] city shootings were not any more likely to be solved in either city, following the introduction of ShotSpotter,” he said.

Piza didn’t know his own employer has a contract with the company. He said there hasn’t been any research done of the technology on college campuses, so it’s “tough for me to say whether the data supports the investment.”

What next?

Cities like Chicago have stopped using the technology due to concerns over its susceptibility to human error, and its role in the police shooting death of a 13-year-old. In Massachusetts, Somerville is also embroiled in a debate to end its usage, which is funded through federal grants. There are 35 sensors installed across Somerville, according to a letter from Digital Fourth, a civil liberties organization.

Somerville City Councilor-at-Large Willie Burnley Jr. recently introduced an order to discuss the city’s use of ShotSpotter. He said over the past year, he’s heard from the Somerville Police Department that the technology has sent alerts when there are not gunshots and sent police to incorrect locations. He called the situation “incredibly dangerous,” and argued that the technology is pulling police away from people who might actually need help.

“The Somerville Police Department has acknowledged that there have been numerous occasions where ShotSpotter has not been accurate,” he said.

Additionally, Burnley Jr. expressed concern about how the ShotSpotter locations were determined. He said the sensors are concentrated in West East Somerville and Winter Hill, particularly near a housing complex where low-income residents live.

“I am personally quite concerned about the impact on civil rights and civil liberties,” he said.

GBH’s Hannah Reale contributed to this report.