SpotShotter IPOed earlier this year.

Time Magazine recently had a very detailed article on them. A few noteworthy details:

ShotSpotter's key pitch is that gunfire is vastly underreported. Research from Jennifer Doleac, a professor of public policy at the University of Virginia, found that 88% of gunfire incidents picked up by sensors in Oakland and Washington, D.C., weren't reported to 911. The main reason: residents don't trust the police.

Any potential study is complicated by ShotSpotter's refusal to release its data. Every shot registered by its sensors is owned by the company. Anyone wanting to fully analyze gunfire patterns must pay ShotSpotter for the information--a decision Clark defends on the grounds that the data is too valuable to give away.

Back at ShotSpotter's office-park HQ, the analysts are monitoring potential gunfire from across the country. The alerts come in almost every minute: a power-line crackle in North Palm Springs, Calif., a strange cracking noise in Newark, N.J., a pop-pop-pop in San Francisco. All apparently harmless. Then came one they were trained for: another shooting in Milwaukee, this time 19 rounds.