The gunfire-detection technology used by Cambridge police is a form of constant surveillance, a federally funded network of microphones that “are always listening,” has a high false alarm rate and is an ineffective use of police resources, residents and experts said at a Wednesday meeting at City Hall.
The ongoing deployment of SoundThinking’s technology, also known as ShotSpotter, was the subject of a City Council Public Safety Committee meeting. At least 30 people addressed the committee of chair Ayah Al-Zubi and councillors Marc McGovern, Patty Nolan, E. Denise Simmons and Jivan Sobrinho-Wheeler.
Resident Shelley Raymond used her time to say “Public safety depends on public trust.”
“If we’re serious about being a sanctuary city, we must ensure that our policies reflect that in practice,” Raymond said. “That means rejecting tools that erode public trust and instead investing in approaches that strengthen community safety, like housing stability, mental health resources and youth programs.”
According to the Cambridge Police Department’s policies and procedures manual of January 2025, ShotSpotter is “intended to enhance the department’s ability to respond effectively to and investigate violent crime involving gunfire.”
The technology uses acoustic sensors placed in selected areas that can detect, locate and alert police to gunshot incidents. For ShotSpotter to be activated, there needs to be an explosive noise, or sound, measuring 120 decibels or greater that hits three or more sensors. For comparison, a human voice averages 60 to 65 decibels.
The pilot program for the surveillance technology was approved by the City Council in 2014. All the initial costs were paid for as part of the Urban Area Security Initiative Grant Program, a more than $1 billion federal Homeland Security program that provided grants to “eligible high-risk urban areas.”
The ShotSpotter technology was deployed before the city passed its surveillance ordinance in 2018, but police submitted the technology to the council for approval in 2019.
Each year, the council approves a surveillance report submitted by city department heads, including the police, that has included ShotSpotter use.
The annual surveillance report was submitted to the council in March and its review is pending before the Public Safety Committee.
Where ShotSpotter is used
During the April committee meeting, police noted that 14 communities in the commonwealth use the technology, including Somerville, Boston, Chelsea, Everett, Holyoke, Lawrence, New Bedford, Revere and Worcester.
Although a map of the service locations was not presented by police commissioner Pauline Wells to the committee to “protect the integrity of the system,” a rough schematic was presented to the June 2025 meeting of the committee.
That service area map for Cambridge showed 29 ShotSpotter locations, with units deployed on the roof of Cambridge Rindge and Latin public high school on Broadway, Roosevelt Towers of the Cambridge Housing Authority at Cambridge Street, among other locations.
The coverage area is approximately 1.25 square miles for several neighborhoods in the city. Any expansion of the system would be done through a public process with input from community stakeholders and come to a council vote.
Contract controls called vague
Gideon Epstein, a Cambridge resident and policy counsel at the American Civil Liberties Union of Massachusetts, said the ShotSpotter technology did not meet the city’s standard for continued use.
“The surveillance technology ordinance explicitly covers gunshot detection technology, and under Section 2.128 of the ordinance, the council must reassess two questions, whether the benefits outweigh the costs, and whether reasonable safeguards exist for civil rights and civil liberties,” Epstein said.
He expressed concerns with the language of the SoundThinking contract that he said was vague in addressing control, retention and use of and access to the collected data, including by federal agencies.
“I encourage the City Council to end its relationship with SoundThinking and remove the sensors,” Epstein said.
Police perspective
Wells told the committee that the system provided prompt notifications to law enforcement, which facilitated a faster response. She was accompanied to the meeting by superintendent of support services Frederick Cabral and deputy superintendent for the criminal investigations section John Boyle.
Since 2018, Wells said the system has outperformed 911 calls.
“Traditional 911 calls are dependent on people taking action,” Wells said. “From 2015 to present, there have been 11 confirmed shootings that were detected by ShotSpotter but did not result in any 911 calls.”
There have also been gunfire incidents reported to police by 911 calls and not detected by ShotSpotter technology.
Wells also said conversations are not recorded by the technology, that there has never been a use of force or community complaints resulting from a police response to a ShotSpotter alert and that U.S. Immigration and Customs Enforcement has not requested the data.
“We will not, do not and have not shared information with ICE or any federal agencies,” Wells said. “Release of any such data would require a judicial subpoena and be limited to a specific criminal investigation of a gunshot incident because that’s all it records.”
Committee member’s worry
Public and community safety was top of mind for McGovern.
“If we were to get rid of ShotSpotter, I’m not sure we’d be any less safe in the community,” he said. “I am worried about who owns the information, who they share that with and what they do with that information, especially in the climate that we’re in right now.”
McGovern said it was time for the city to decide the issue.
“We owe it to the public to make some sort of the decision,” he said.
The Public Safety Committee next meets at noon May 20 at City Hall, 795 Massachusetts Ave., Central Square.
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