May 3, 2021

ShotSpotter Generated Over 40,000 Dead-End Police Deployments in Chicago in 21 Months, According to New Study

MacArthur Justice Center study finds City’s use of ShotSpotter is inaccurate, expensive and dangerous

CHICAGO – A new study of Chicago’s use of ShotSpotter, a surveillance system designed to detect gunfire, finds that the vast majority of alerts generated by the system turn up no evidence of gunfire or any gun-related crime. Instead, the ShotSpotter system sends police on thousands of unfounded and high-intensity deployments, which are focused almost exclusively in Black and Latinx communities. The complete findings of the study can be found at

“Surveillance technology has a veneer of objectivity, but many of these systems do not work as advertised, ” said Jonathan Manes, an attorney with the MacArthur Justice Center, who spearheaded the study. “High-tech tools can create a false justification for the broken status quo of policing and can end up exacerbating existing racial disparities. We needed to know whether this system actually does what it claims to do. It does not.”

ShotSpotter blankets neighborhoods with microphones in order to attempt to detect and locate the source of gunfire. It sends alerts of supposed gunfire immediately to local police.  ShotSpotter claims to be 97% accurate. However, ShotSpotter has not released any scientifically-valid study to substantiate that figure. There are also no studies testing whether ShotSpotter can reliably tell the difference between the sound of gunshots and other noises like firecrackers, backfiring cars, construction noises, helicopters, and other loud, impulsive sounds.

The study conducted by MacArthur Justice Center at Northwestern Pritzker School of Law reviewed ShotSpotter deployments for roughly 21 months (from July 1, 2019 through April 14, 2021) using data obtained from the City of Chicago. Their analysis found that 89% turned up no gun-related crime and 86% led to no report of any crime at all. In less than two years, there were more than 40,000 dead-end ShotSpotter deployments.

“Our findings are shocking,” said Manes. “The ShotSpotter system in Chicago prompts thousands of deployments by police hunting for gunfire in vain. This system puts police on high alert and sends them racing into communities; but almost nine times of our ten, the police don’t turn up evidence of gun crime or any crime at all. It creates a powderkeg situation for residents who just happen to be in the vicinity of a false alert.”

The study is also the basis of an amicus brief filed today in support of a motion by the Cook County Public Defender that challenges the scientific validity of the ShotSpotter system’s gunfire reports, which prosecutors have attempted to use as evidence in a criminal prosecution.

The amicus brief was submitted on behalf of a coalition of community-based organizations that are concerned about the impact of ShotSpotter on overpoliced and underresourced communities of color on the city’s South and West sides. Those organizations are Brighton Park Neighborhood Council, Lucy Parsons Labs, and Organized Communities Against Deportations (OCAD).

“Knowing very well that police officers tend to escalate all types of situations and are known to use excessive force, the ShotSpotter technology creates an additional layer of violent response from police officers as they rush aggressively to poor, Black & brown neighborhoods expecting to be met with gunfire,” Miguel Lopez, Membership Coordinator for OCAD. “If the city was really serious about stopping gun violence, they would listen to the community and use those $33 million dollars to invest in those communities in order to create the social environment where young people would have the transformative tools to deal with conflict.”

The City of Chicago has deployed ShotSpotter only in the police districts with the highest proportion of Black and Latinx residents. On an average day, there are more than 61 ShotSpotter-initiated police deployments that turn up no evidence of any crime, let alone gun crime. Neighborhoods that are surveilled by ShotSpotter are subject to thousands of additional, unfounded police deployments just because the ShotSpotter system is present.

Every unfounded ShotSpotter deployment creates an extremely dangerous situation for residents in the area. ShotSpotter primes police to believe that they are heading to a dangerous location where a person has just fired a gun. Any resident who happens to be in the vicinity of a ShotSpotter alert will be a target of police suspicion or worse. These volatile deployments can go wrong in an instant.

“Only residents in predominantly Black and Latinx neighborhoods have to contend with the burden of thousands of unnecessary and potentially dangerous police deployments,” said Manes. “Only their neighborhoods get saddled with inflated statistics about supposed gunfire. At the same time, there is no evidence that the ShotSpotter system makes communities safer or reduces crime.”

CPD publicly promotes ShotSpotter as an essential tool for crime prevention, but there is no evidence that it reduces crime. Academic studies of ShotSpotter and similar gunshot detection systems have found that they do not reduce the number of violent crimes and do not even reduce the number of confirmed shooting incidents identified by police. Instead, the studies find that the main effect of ShotSpotter is just to increase the number of times police are deployed.

The Chicago Police Department has a long history of excessive force, illegal and discriminatory stop-and-frisk, and other abusive policies and practices. ShotSpotter reinforces and may exacerbate this system of racialized policing.

CPD requires managers to incorporate ShotSpotter data into its CompStat reports, which are used to hold commanders accountable to performance targets. ShotSpotter data also feed into the city’s “predictive policing” technology. The inflated gunfire statistics generated by ShotSpotter in predominantly Black and Latinx neighborhoods will thus skew how the police allocates its resources, unless the city is taking careful steps to eliminate the effects of unfounded ShotSpotter alerts. These statistics can create a false “techwash” justification for racialized patterns of policing.

“Like many surveillance systems, CPD’s use of ShotSpotter trades on a veneer of objectivity but, in practice, it reinforces racial disparities in policing,” said Manes. “The City should be investing in communities and in solutions that work, not in police technologies that create faulty justifications for ever more policing.”

In 2018, the City of Chicago entered a $33 million, three-year contract with ShotSpotter. Over the past two years, the City has paid ShotSpotter about $10 million per year and spends untold additional resources on police officers chasing down tens of thousands of unfounded ShotSpotter alerts every year. The City of Chicago is one of ShotSpotter’s two largest customers, accounting for 18% of its annual revenue in 2020. The City of Chicago’s contract with ShotSpotter expires August 19, 2021 unless the city exercises its option to extend.

The complete findings of the study, including the legal brief filed in court, can be found at