ShotSpotter is a system Oakland Police Department uses to detect and locate gunfire in the city. Oakland has been using it on and off since 2006. The system covers much of the city, though neither the city nor the company that makes the system will disclose where individual sensors are for security reasons. We do know that they tend to be put high above the ground on roof tops and utility poles.
ShotSpotter works by listening for the sounds of gunfire. Computers can then calculate where the gunfire came from by measuring the difference between the times that the sounds arrive at the sensors. Some privacy advocates have worried that the police could abuse what is essentially a city-wide microphone system to eavesdrop on private conversations. The system's manufacturer states that the sensors only activate on the sounds of gunfire or similar noises like fireworks.
A new kind of ShotSpotter with indoor capabilities is reportedly being piloted an Oakland charter school (apparently the Oakland School for the Arts). Ann Campbell Washington, an Oakland Unified School District board member (which doesn't govern charter schools), has said that money would be better spent on more security officers. Jody London, another OUSD Board member, states that it would not make sense to spend District money on this program given how rare such incidents are, and would instead spend the money on counselors.1
Public Records released about ShotSpotter:
Articles about ShotSpotter:
2012-05-28: Shots Fired, Pinpointed and Argued Over New York Times
2013-11-11 ShotSpotter offers gunfire detection to Bay Area schools after mass shootings San Jose Mercury News