Cambridge hearing exposes split over police use of ShotSpotter (Sound Thinking)

The Cambridge Public Safety Committee on May 21 held a public hearing to review the Cambridge Police Department’s 11‑year use of ShotSpotter gun‑detection technology, now branded Sound Thinking, bringing sharply divergent views on whether the system improves response times or creates unacceptable surveillance risks.

The hearing featured presentations by Cambridge police officials and a company representative, followed by an academic critic and technical expert. Police and the district attorney described examples in which alerts preceded 911 calls and assisted rapid responses; researchers and public defenders questioned the company’s claims, the completeness of the data and whether recordings or retained data could be shared beyond the city.

Cambridge Police Commissioner Christine Elo said the department views ShotSpotter as a tool, not “a fix all,” and described cases in which alerts arrived before 911 calls and officers reached victims or recovered evidence faster than they otherwise would have. Acting public information officer Bob Reardon briefed the committee on the system’s local footprint: Cambridge’s ShotSpotter coverage is about 1.255 square miles and has been funded by the Urban Areas Security Initiative (UASI); he told the committee the city’s UASI grant covers a roughly $50,000 annual contract cost.

The department presented its recent incident counts and system performance for committee members. CPD slides summarized 2023 as having six confirmed shootings citywide (all inside the ShotSpotter coverage area), with four incidents identified by ShotSpotter and four additional ShotSpotter activations that could not be confirmed as shootings. For 2024 the slides listed 15 citywide shooting incidents, 11 of them in the coverage area; of those 11 the department said five produced ShotSpotter activations and three more activations were not confirmed as shootings. A year‑to‑date slide to May 21 showed four confirmed shootings (three in the coverage area) and three additional ShotSpotter activations that the department had not been able to verify.

Representatives of Sound Thinking defended the product’s contribution to situational awareness and said the company’s incident review center typically delivers a location estimate within 60 seconds and a spatial radius the company describes on its materials as roughly 82 meters (the company representative also referenced a 25‑meter radius figure in the presentation). The company speaker said customers receive one second of audio before a detected gunshot event and one second after the event in an alert package sent to the police department and described privacy changes the firm has made over time.

Boston University political scientist Spencer Piston, who titled his presentation “Forensic Snake Oil,” urged councilors to treat the company’s marketing claims skeptically. Piston cited academic studies (including a longitudinal study led by Eric Pisa) that he said found no significant reduction in gun homicides attributable to ShotSpotter and cited published investigations that reported high percentages of unfounded alerts in other cities. He also said public records requests and other transparency efforts had been limited and urged the city to make raw data available for independent review.

Technical testimony from Rob Maher, an electrical and computer engineering professor, noted microphones intended to capture distant gunfire can, depending on placement and gain, be capable of picking up nearby speech; Maher said that capability is a technical reality even if agency practices limit what audio is released to police.

Criminal defense attorney Connie Tran told the committee the police slide deck’s “real world example” of an August 2022 incident was misleading in ways that mattered in court. Tran said she was the defense counsel in the cited case and that a jury acquitted her client of firearms charges; she told the committee the post‑event forensic review that appears in the department’s slides occurred up to 18 months after the alert and that expert testimony at trial contradicted some claims in the city presentation.

District Attorney Marianne Ryan said ShotSpotter is an investigative tool, not a sole basis for prosecution, and argued the system can produce evidence or lead investigators to victims or ballistic material they might otherwise miss. “We can’t lose sight of the value of having as many tools in our toolbox as are possible,” Ryan told the committee.

Committee members pressed several recurring themes: whether the sensors or retained audio could be shared beyond the police department; why sensor locations remain undisclosed (police said publication could enable tampering); the program’s cost and federal funding; and the system’s ratio of unconfirmed alerts to confirmed shootings. Commissioner Elo and police staff said the city had not found complaints linked to ShotSpotter activations in Cambridge over the past 11 years and said the department has not used listening capabilities for intelligence or voice surveillance.

Public comment following the presentations was overwhelmingly critical. Dozens of speakers—residents, public defenders, mental‑health clinicians and local activists—urged the council to end the contract, citing research questions, high false‑alarm rates reported elsewhere, data‑ownership provisions in the contract and fears that the data could be used by federal agencies. Multiple commenters said the company and its representatives were motivated by profit and urged the city to redirect resources toward proven public‑health interventions, services and violence‑prevention programs.

Councilors and staff agreed on at least two staff actions coming out of the hearing: the police department will explore whether a public ShotSpotter dashboard or other ways to increase transparency are feasible, and the city solicitor will review contract and data‑access provisions and report back to the committee. The committee did not take a vote on whether to continue, expand or terminate the ShotSpotter contract.

The discussion is expected to continue: councilors asked for the company and the police to provide written materials, and committee members said they want clearer contract language and raw data access before any further policy steps are taken.