86% of alerts from city’s gunshot detection system led to ‘dead-end deployments,’ researchers find

More than 40,000 ShotSpotter alerts prompted no formal reports of any crime over a 21-month stretch — amounting to an average of 61 unfounded deployments each day.

SHARE 86% of alerts from city’s gunshot detection system led to ‘dead-end deployments,’ researchers find
Chicago police Capt. Steven Sesso operates a ShotSpotter gunshot detection system in the 11th District.

Chicago police Capt. Steven Sesso operates a ShotSpotter gunshot-detection system in the Harrison District.

Frank Main/Sun-Times file

An analysis of the city’s gunshot detection system released Monday found that nearly 86% of police deployments to alerts of gunfire prompted no formal reports of any crime.

The research, conducted by the MacArthur Justice Center at the Northwestern University School of Law, shows there were more that 40,000 “dead-end deployments” to gunshot alerts recorded between July 2019 and mid-April — an average of 61 each day.

Just 10% of the alerts over that period sent officers on calls that likely involved guns, the researchers found after analyzing records kept by the city’s Office of Emergency Management and Communications.


ShotSpotter, the publicly traded company that provides its acoustic gunshot detection technology to Chicago and 110 other cities across the country, claims its system is a “highly effective technology” that’s 97% accurate. During a news conference Monday, Mayor Lori Lightfoot called ShotSpotter “an incredibly important tool in our crime-fighting arsenal” and questioned whether the new research is “actually accurate.”

Meanwhile, activists continue to raise concerns about ShotSpotter’s ability to distinguish between gunfire and other loud noises like fireworks. In addition, alarms are being sounded over the technology’s potential to increase the number of highly charged law enforcement interactions in police districts with large minority populations.

“It sends police racing into communities searching, often in vain, for gunfire,” said Jessey Neves, a spokeswoman for the MacArthur Justice Center. “Any resident in the area will be a target of police suspicion or worse. These volatile deployments can go wrong in an instant.”

Lissa Druss, a spokeswoman for ShotSpotter, defended the technology but acknowledged that the company hasn’t reviewed the findings of the new study.

“ShotSpotter technology is incredibly accurate, alerting officers to the exact location of gunfire incidents in less than 60 seconds, finding victims who need assistance, getting them medical aid faster [and] saving lives,” Druss said.

The Chicago Police Department’s relationship with ShotSpotter began in 2012 when the technology was implemented to cover a small portion of the city. That reach expanded to over 100 square miles when the department entered into a new $33 million contract in 2018, at which point ShotSpotter described the city as its “largest customer.”

With the current contract set to expire in August, Lightfoot said CPD officials have continued to evaluate the arrangement to ensure the city is “getting the best bang for our buck.”

The mayor told reporters that ShotSpotter is a “life-saver” when paired with other technology at the CPD’s Strategic Decision Support Centers, crediting the combination with helping raise this year’s homicide clearance rate.

“In an environment where people are fearful sometimes of calling 911 for a variety of reasons, ShotSpotter allows us to understand that … those challenges exist that are out there,” she said. “So where the calls for service don’t come, we still are able to respond.”

The Police Department’s use of the gunshot detection technology has drawn increased attention after the death of 13-year-old Adam Toledo, who was fatally shot by an officer responding to ShotSpotter alerts in late March. Freddy Martinez, executive director of the transparency nonprofit Lucy Parsons Labs, penned an op-ed last week in South Side Weekly calling for an end to the city’s deal with ShotSpotter in the wake of his killing.

“We must work to abolish the use of surveillance technologies to bring justice for Adam Toledo and others like him,” Martinez wrote.

On Monday morning, Martinez’s group and two other nonprofits filed an amicus brief in a pending murder case in Cook County court that relies on ShotSpotter evidence. The MacArthur Justice Center is representing the organizations behind the filing, which draws on the new findings about ShotSpotter.

The defendant, 64-year-old Michael Williams, has pleaded not guilty to six counts of murder stemming from a fatal shooting on the South Side that happened amid a wave of looting late last May. Williams, who was denied bail, already filed a motion April 22 to exclude the ShotSpotter evidence, court records show.

Spokespeople for the Cook County state’s attorney’s office declined to comment on the pending case. So did officials in the Cook County public defender’s office, which is handling Williams’ defense.

Monday’s filing piggybacks on Williams’ motion and urges the court to scrutinize ShotSpotter’s reliability given that the technology has “far-reaching consequences beyond this single case.” They note that other cities have dropped ShotSpotter “because the system sent their officers out on too many wild goose chases.”

Citing the technology’s “significant, cross-cutting consequences for the legal rights of Chicagoans” and the lack of any “meaningful judicial scrutiny” in Illinois, the groups asked the court “to take seriously its duty to investigate and ascertain the reliability of reports of gunfire that ShotSpotter generates.”

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