A high-density urban environment such as Chicago requires up to two dozen strategically placed microphones per square mile. The system’s accuracy is generally within 65 feet in cities, as opposed to 10 feet in flat, open spaces, because acoustic waves “bend” around buildings, said Showen, who previously worked at SRI International and the Arecibo Observatory in Puerto Rico. ShotSpotter claims that cities that use it see illegal gunfire plummet by an average of 35 percent within two years.
Local media and some national outlets have reported on the expansion of gunfire-detection technology in Chicago. But there is little in the way of independent research supporting ShotSpotter’s claims about decreasing gun violence—or any other positive outcomes for that matter. This may be why CPD ignored my email requests to interview their chief technology officer to discuss ShotSpotter’s outcomes and its expansion in Chicago.
Jennifer Doleac is one of the very few academics who has studied ShotSpotter. She’s an assistant professor of public policy and economics at the University of Virginia who specializes in the economics of crime and how technology impacts public safety. “There is very good evidence that this technology detects gunfire,” she told me when I asked her about CPD’s claims that ShotSpotter was behind the decrease in shootings. “But does it have an impact on anything that we care about, such as saving lives by getting victims to the hospital faster, clearing more cases, reducing crimes, or decreasing gun violence? We have no evidence.”
More than 90 cities nationwide use ShotSpotter despite the lack of independent analysis. And in fact, there are hints that the technology doesn’t deliver meaningful benefits. The Charlotte-Mecklenburg Police Department ended its four-year contract in February 2016 because it “wasn’t successful in identifying or prosecuting the people who fired the shots picked up by the system,” according to a memo obtained by The Charlotte Observer.
True evidence for or against ShotSpotter’s ability to decrease gun violence is lacking for one key reason: The company’s data is proprietary and closely guarded. Doleac, who also directs UVA’s Justice Tech Lab, was able to obtain ShotSpotter data in two cities—Washington, D.C., and Oakland, California—through the Freedom of Information Act to study the impact of juvenile-curfew laws and reported versus actual levels of gunfire.
The data that Doleac obtained confirms what police and violence researchers have said for decades, namely, that only a fraction of gunfire is reported to 911. Only about 12 percent of all gunfire was reported to police in D.C. and Oakland, according to a study she conducted with the Purdue University economist Jillian Carr.
At the very least, one could expect that gunfire-detection systems could decrease police response times, Doleac told me when we chatted in November. But it’s difficult to home in on this or any other specific outcome because ShotSpotter owns the gunshot data that its sensors collect in each city. Clients are prohibited from releasing data to the public, news media, or researchers.