Jennifer Doleac is one of the very few academics who has studied ShotSpotter. She’s a UVA assistant professor of public policy and economics 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 the Chicago Police Department’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...