Against the backdrop of daily immigrant arrests in Massachusetts and nationwide come sharper objections to ShotSpotter gunfire-detecting technology in Cambridge: Residents fear the microphones are listening to them talk, and that the federal government will be handed the recordings.
ShotSpotter, a tool used by police to listen for shootings, is paid for by the Department of Homeland Security. Each fact drew attention Monday at a meeting of the City Council’s Public Safety Committee.
Even city officials expressed discomfort over the relationship.
“We live in a strange time where there’s the worry that someone may procure the information,” city councillor Cathie Zusy said. “I wonder if we should take it down, and then, once the world returns to a normal, safer place, then reconsider resuming use of the technology if we find that there actually is a need for it.”
Cambridge is one of more than a dozen communities in Massachusetts with the microphones, along with Somerville, Boston, Worcester and Northeastern University, according to a police presentation at the meeting. An Urban Area Security Initiative grant from the DHS pays for ShotSpotter in Metro Boston cities, including the $50,000-a-year cost in Cambridge, police commissioner Christine Elow said.
In Cambridge, the technology is entirely located in The Port and Riverside neighborhoods, neighborhoods that have the highest concentration of Black, brown, low-income and immigrant residents, said Stephanie Guirand, a core team member of the organization The Black Response, in an interview. (SoundThinking, the company behind ShotSpotter, does not reveal the precise locations of its devices to police or the public, but data leaked to Wired.com allowed the group to map their placement.)
That the microphones are in areas of larger immigrant populations is a coincidence – they were placed in 2014 based on historical crime data about where there had been gunfire in Cambridge, said a police spokesperson, Robert Reardon, during the meeting.
The department has “absolutely not” used ShotSpotter’s listening technology to record voices, and does not intend to, Elow said.
Surveillance possible, but not the practice
Only gunshotlike sounds activate ShotSpotter alerts, said Alfred Lewers Jr., vice president of community engagement and trauma response at SoundThinking, who spoke at the meeting. Lewers said he has never heard human voices in the recordings of gunfire or in the one second of audio pre- and postgunfire that SoundThinking shares with customers.
That is not to say voice surveillance is impossible: New York University Policing Project did a privacy audit of ShotSpotter in 2019 – linked to on a SoundThinking page of frequently asked questions – that concluded the technology could conceivably capture the voices of individuals near devices but has an “extremely low” possibility of being used for targeted voice surveillance, Lewers said.
Robert Maher, professor of electrical engineering at Montana State University, testified Monday. “The microphones are going to try to pick up the sound of gunfire that might be as much as 2 miles away from the location,” Maher said. “So typically, the gain, or the microphones’ amplification, is set to pick up what may be relatively quiet sounds when a gun is so far away from the location. It’s certainly possible, depending on the placement of the microphone, that it could potentially record conversations of individuals nearby. Now, clearly the intent of ShotSpotter is not to do so,” Maher said, “but it’s technically capable.”
SoundThinking purges all audio other than gunshots routinely, according to its overview of the audit. The overview did not specify how often these purges occur.
“Somebody is getting that data”
The company’s agreement for use in Cambridge also says ShotSpotter data is the “sole and exclusive property” of SoundThinking, which can “use any and all data for any purpose.”
That didn’t calm residents’ fears.
“ShotSpotter is financed by the Department of Homeland Security. Why would DHS want more surveillance in our communities if not to further its own agenda in this political moment?” a Somerville resident asked during public comment.
Zusy had concerns too. “Somebody is getting that data – and you’re not working for us, you’re working for the Department of Homeland Security,” Zusy told Lewers.
The company representative pushed back, saying SoundThinking does not and “will not give the information – any information – to any entities outside of the actual customers.”
But again there was an exception: Lewers said SoundThinking can share ShotSpotter data if it gets permission from the police department – where officials might allow data to be shared so a contiguous jurisdiction can help respond to an alert, for example.
Sanctuary city with a surveillance law
Cambridge is a sanctuary city where the policy is for officers to do their own work, not do the work of federal agents; several meeting participants brought up the contradictions between the city holding sanctuary and welcoming status yet employing DHS-funded devices that record audio in Bipoc and immigrant neighborhoods.
The city also has a surveillance ordinance that vice mayor Marc McGovern described as “pretty thorough.” Cambridge adopted the ordinance in 2018 and let the ShotSpotter program stay in place.
In addition to the potential for government eavesdropping, some meeting attendees raised concerns about interactions between police and Black and brown residents of Cambridge resulting from ShotSpotter alerts. Spencer Piston, an associate professor of political science at Boston University, pointed out during testimony that alerts send police “primed to expect an active threat” into marginalized communities, even though some ShotSpotter alerts are false.
“As the history of policing in black communities really makes painfully clear, these technologies are likely to increase unnecessary police interactions,” said Lorenzo Bradford, a core team member of The Black Response.
Elow said that police could find no complaints or arrests with direct links to a ShotSpotter activation, though.
Occasional benefits
Police said there were three times in 2023 and 2024 when police arrived at the scene of gunfire faster for a ShotSpotter alert than if officers had waited for a 911 call. One of these incidents involved a victim with a “serious” gunshot wound. The timely arrival and medical attention “quite possibly saved that individual’s life,” Reardon said.
Nine total confirmed shootings in Cambridge were accompanied by ShotSpotter activations in 2023 and 2024, according to the presentation. Forty percent of ShotSpotter activations in Cambridge were tied to confirmed incidents of gunfire, compared with 28 percent of 911 calls reporting possible gunfire.
https://embed.documentcloud.org/documents/25966119-250606-shotspotter/?embed=1
But the system has sent false alarms and missed incidents: Cambridge saw 15 confirmed shooting incidents last year, 11 of which fell within ShotSpotter’s coverage area, and only five resulted in an activation.
Cambridge’s ShotSpotter is 50 percent accurate, with a 58 percent false positive rate and a 48 percent false negative rate, according to data analysis by The Black Response from eight years of police department BridgeStat presentations. False positives refer to ShotSpotter alerts with no evidence found that a gun had fired; false negatives are gunfire events that do not trigger a ShotSpotter alert.
Just one tool
Elow stressed that police use ShotSpotter as one tool among many in their approach to community safety, and not one she wanted to give up.
The Black Response saw less value in the technology.
“ShotSpotter is not a magical solution to gun violence,” Guirand said during public comment Monday. “It is simply a microphone, and I do not believe it is worth trading people’s right to privacy to allow a company or the federal government to record our communities at all times in exchange for the possibility that a police officer might get to a scene of gunfire faster.”
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Not to the core point of this relevant piece, but: Is it true that those neighborhoods have the largest immigrant populations? Cambridge has a lot of immigrants throughout no? The Census Bureau estimates over 22% of residents of Middlesex County are foreign born.
We already have enough surveillance in modern society and don’t need more, especially now that Trump and DHS Secretary Noem are the ones surveilling. Take it down.
Cambridge was quite safe before ShotSpotter came along. It will be quite safe without it now.
Cambridge needs many more CCTV cameras.
In addition to all the other concerns already mentioned, Shotspotter famously doesn’t even work. It mistakes every loud noise for a gunshot. Cops are simply addicted to wasting money.
The police wasting money? I’m afraid you’re looking in the wrong place. The police serve this city very well. You’ll find that out when you really need them.
This city is addicted to commissions and advisory boards, all of which require city employees in some fashion or other.
Just a couple to mention: Peace Commission; Commission on the Status of Women; Language Justice Division, and so many more.
This city needs to cut out wasteful spending.
Presented with an example of police wasting resources on an overhyped tech with racist applications and questionable utility… “The police wasting money? I’m afraid you’re looking in the wrong place.” Sure…
I’m in favor of peace, women, and language justice, so I don’t have a problem with any of those commissions. All seem like better uses of money than buying another toy for our overpaid cops.