Ahead of an upcoming Boston City Council hearing about its controversial gunshot detection technology, the company SoundThinking is roiled in a discourse match with elected officials and the American Civil Liberties Union of Massachusetts about whether its product is effective and accurate, or a violation of civil rights.

This week, SoundThinking contested assertions from Massachusetts legislators that its ShotSpotter technology may violate the Civil Rights Act of 1964, something mentioned in a May letter to the Department of Homeland Security.

“I am concerned that your understanding of ShotSpotter is based on numerous recycled falsehoods and misleading assertions that do not hold up to hard facts and accurate information,” wrote Ralph Clark, the company’s president to legislators and the Department of Homeland Security in his own letter on June 10. He said ShotSpotter was created to bridge gaps in the 911 reporting system to get police to shooting incidences and aid gunshot wound victims.

Over a dozen communities in Massachusetts currently use ShotSpotter, as does Northeastern University.

Clark claimed a few cities across the country have chosen to not renew their contracts with SoundThinking, but said none had made that decision because of “alleged civil rights violations.” The ACLU of Massachusetts strongly contests that assertion, pointing to an ongoing debate in Chicago to end the its contract after September.

In the May letter, four legislators said ShotSpotter’s sensor placement in Black and Brown communities could be contributing to overpolicing, basing some of their research around an ACLU of Massachusetts report. The legislators — Sen. Ed Markey and Elizabeth Warren from Massachusetts, Sen. Ron Wyden from Oregon, and Rep. Ayanna Pressley from Massachusetts —demanded that the Department of Homeland Security investigate the technology.

Neighborhoods surveilled by the devices are often comprised of low-income, and Black and Brown residents, according to a WIRED analysis of leaked data. In his letter this week, Clark wrote that geographic decisions are “color-blind” and based on empirical data. He said residents, regardless of race, benefit from the technology.

“If you read headlines across the country and you can subtract out those pieces that are merely opinion, what you will see reflected over and over again is ShotSpotter locating gunshot wound victims, leading police to arrest offenders,” said Tom Chittum, SoundThinking’s senior vice president of analytics and forensic services.

“And it’s not because this technology simply gets lucky. It’s because it really works,” he said.

While SoundThinking didn’t answer questions about the Boston Police Department contract, it pointed to a June 1 Roxbury shooting that set off an alert. Officers found shell casings, video evidence of a shot fired, and seized multiple firearms after, the company wrote.

Chittum said that legislators and the ACLU of Massachusetts have been invited to visit the company’s D.C.-based Incident Review Center to see a demonstration of the technology.

Kade Crockford, director of the Technology for Liberty Program at the ACLU of Massachusetts, said several independent analyses — including an investigation by the Chicago Office of the Inspector General — show that ShotSpotter has “significant flaws.” The ACLU of Massachusetts’ report said that in nearly 70% percent of ShotSpotter alerts in Boston from 2020-2022, police found no evidence of gunfire.

“A range of examples exists to demonstrate the technology’s flaws, including but not limited to reports of fireworks at a birthday party, backfiring dirt bikes, and a metal plate in the road mistaken for gunshots,” said Crockford.

Chittum referred to one claim in the ACLU of Massachusetts’ report that mentioned a piñata triggered the technology, which was later found by The Boston Herald to be erroneous. That claim has since been removed from the report, the ACLU said.

“While a mention of a birthday celebration piñata was included in a police report provided to the ACLU in response to a public records request related to ShotSpotter use, a subsequent review confirmed that the technology was not triggered in that particular instance,” said Crockford. The organization stands by its overall assessment of the technology’s effectiveness.

Meanwhile, legislators are doubling down on the effort for a federal probe.

“There are serious, well-documented concerns about the use of federal funds to support a technology that may contribute to unjustified surveillance and over-policing of minority communities, and violate the Civil Rights Act,” wrote a spokesperson for Markey in a message to GBH News.

“We have asked the Department of Homeland Security to investigate the situation with ShotSpotter, and we look forward to the Department’s response.”