Research shows the technology doesn’t reduce shootings or increase clearance rates, but it may have other benefits
On February 13, Chicago Mayor Brandon Johnson announced that the city’s ShotSpotter gunshot detection system would be discontinued, with a phasing out of the technology set to begin this September. ShotSpotter is the global leader in gunshot detection technology — a network of acoustic sensors that pinpoints the location of gunfire and typically alerts the police quicker than 911 calls. SoundThinking, ShotSpotter’s vendor, reports that over 250 agencies worldwide (including the NYPD) have adopted their platform. Chicago initially installed ShotSpotter in September 2012 within an approximately three-square-mile area, with coverage expanding to 136 square miles by May 2018. Annual costs advertised on the SoundThinking website ranged from $8.8 to $12.3 million per year for maintaining this coverage.
In the leadup to his decision, Johnson cited concerns that ShotSpotter was unreliable, overly susceptible to human error and played a pivotal role in the police killing of 13-year-old Adam Toledo. Critics say the cancellation was politically motivated and insist ShotSpotter is a vital policing tool. Regardless of political motivations, an honest review of the research evidence suggests the decision to cancel ShotSpotter makes sense.
In 2019, my colleagues and I were awarded a grant from the National Institute of Justice to evaluate the effect of ShotSpotter in Chicago and Kansas City. Incorporating more than 15 years of crime, calls for service and police enforcement data, our study is the largest evaluation of the technology to date. We incorporated a matched quasi-experiment, meaning that the ShotSpotter areas were compared to control areas that shared relevant characteristics but were not covered by ShotSpotter. Such similarity between the ShotSpotter and control areas helped ensure we made “apples-to-apples” comparisons in our analysis.
We submitted our preliminary research findings to NIJ in the summer of 2023. Results of the Kansas City evaluation have since been published across three journal articles; the Chicago results are currently undergoing peer review. In full transparency, I presented results to Chicago city officials before the decision to cancel the ShotSpotter contract. I do not know how much my presentation influenced the thinking of the Johnson administration; my presentation occurred only a couple of weeks prior to the announcement of the cancellation.
Regardless of political motivations, an honest review of the research evidence suggests the decision to cancel ShotSpotter makes sense.
Our research in Chicago found that police officers stopped their patrol cars more often and closer to the location of reported gunfire when responding to ShotSpotter alerts than 911 calls, as measured by GPS coordinates of patrol vehicles. The recovery of illegal firearms increased in police districts covered by ShotSpotter, particularly at the scenes of fatal shootings. However, ShotSpotter did not reduce the occurrence of shots-fired calls for service, fatal shootings, non-fatal shootings or other violent felonies committed with firearms. The introduction of ShotSpotter in police districts had no impact on gun-violence crime clearance rates (the proportion of cases solved by police).
Our analysis in Kansas City generated similar findings. Police officers similarly stopped their patrol cars more often and closer to the location of the reported gunfire on ShotSpotter runs. The collection of ballistic evidence and recovery of firearms increased in the ShotSpotter coverage area. While shots-fired calls for service decreased in the ShotSpotter area of Kansas City, no crime types involving confirmed victims (shootings, robberies or aggravated assaults) saw changes. ShotSpotter did not improve gun violence clearance rates there either.
We were able to compare the reporting time and spatial accuracy of ShotSpotter and 911 calls for service in Kansas City, but not Chicago, due to data availability. Our analysis found that in Kansas City, ShotSpotter alerts occurred a median of 93 seconds before the first 911 call for service. ShotSpotter alerts and 911 calls were reported as occurring on different non-intersecting streets in more than 26% of cases, meaning ShotSpotter provided more accurate locations compared to 911 calls. However, shots-fired incidents in Kansas City’s ShotSpotter area were more than 15% more likely to be classified as unfounded by responding police officers. While we did not have the necessary data to diagnose the precise reason for the unfounded finding, one possible explanation is that ShotSpotter sometimes inaccurately classifies loud noises as sounds of gunfire.
Any arguments that the cancellation of the Chicago ShotSpotter contract occurred within a low-research environment are misguided.
The findings of our research reflect what’s been reported elsewhere. Research has generally found that ShotSpotter leads to quicker police responses to gunfire events. However, regarding Chicago, a study by Michael Topper and Toshio Ferrazares found that ShotSpotter implementation caused police officers to be dispatched one minute slower to reports of shots fired and to arrive on scene nearly two minutes later. A report by the Bureau of Justice Assistance noted most prior gunshot detection technology studies found no evidence of crime reduction. None of the seven prior investigation evaluations identified by my colleagues and I found evidence that case clearance increased following ShotSpotter deployment. While these findings read as an indictment of the technology, future research should determine if the manner by which police implement and utilize ShotSpotter impacts the likelihood that program goals will be met.
ShotSpotter can have benefits other than the increased collection of ballistic evidence and illegal firearms, even if our research has shown little effect on gun violence or clearance rates. The technology can increase the number of gunshots that receive a police response, which is important given the long-acknowledged problem of unreported crime. It can also facilitate faster deployment of emergency medical services to shooting scenes (though, research by Anna Goldenberg and colleagues found faster EMS deployment did not impact mortality rates for ShotSpotter alerts in Camden, N.J.).
One can argue that Chicago should evaluate whether they are receiving such benefits before making a final decision on the ShotSpotter contract. However, valid research findings on the preventative and investigative benefits of ShotSpotter in Chicago are currently available. Any arguments that the cancellation of the Chicago ShotSpotter contract occurred within a low-research environment are misguided.
The question now turns to what comes next in Chicago’s efforts to combat gun violence. In a recent statement, Johnson’s office stated that from now until September 22, 2024 — when the contract will lapse — police and community stakeholders “will assess various tools, data and programs that build upon increased safety and trust, and issue recommendations to that effect.” The City’s recent People’s Plan for Community Safety similarly lays out goals relating to supporting adults and youth of highest promise, healing trauma in crime victims and addressing root causes of violence. Neither document provides much detail about the specific programs that will help achieve these goals. The City of Chicago would be wise to consult the vast research evidence on what works (and what doesn’t) in crime control and prevention in developing their next phase of public safety investments.