The Bay Area company that on Monday proposed adding its gunshot detection systems to schools has a long relationship with local police departments.

SST, a Newark-based tech company, perplexed some school officials and worried privacy advocates when is offered its ShotSpotter technology for indoor surveillance in schools. But the company has a few fans in its corner -- Bay Area law enforcement.

ShotSpotter has been used for several years in six Bay Area cities. Police say ShotSpotter has helped them respond more quickly to crime scenes and capture suspects, and provide court evidence to solve homicide cases. Oakland police started using the gunshot detection technology in 2006; it now covers 80 percent of the city, said Capt. Ersie Joyner.

East Palo Alto police used ShotSpotter to locate the hot spots of gun violence, and in an effort to reclaim those community spaces, began hosting Zumba classes there. Those exercise classes drove out the gun-wielding criminals. After five months, shootings in the city's new fitness zones were down 40 to 60 percent, said former police Chief Ronald Davis, who left the post just last week.

"The damage of gunfire is not always the victim that gets shot," he said. "It's the damage on the psyche of the community."

Richmond, San Pablo, Redwood City and San Francisco also track gun violence with ShotSpotter.

This year the company began compiling a national gunfire index, offering what some say is the first accurate gauge of gun violence in urban areas.

"It's very reliable and stable," Sarah Lawrence, law and public policy expert at UC Berkeley said of ShotSpotter data. Lawrence has partnered with East Palo Alto police on projects to help reduce crime..

Researchers and public officials are using the data to inform new public policies that address issues such as chronic disease, mental illness and obesity, which can be linked to gunshot violence.

Last year, gunshots rang out more than 4,200 times in a single five-square mile patch of Oakland. In the first six months of 2013, more than 18,700 shots were fired in high-crime areas of 30 cities where SST is collecting data.

"There was a lot of lead up in the air," said SST chief executive Ralph Clark.

The ShotSpotter statistics are more robust than national gunshot data from law enforcement, which draws from 911 calls. According to law enforcement experts, police are lucky to get 20 to 25 calls for every 100 gunshots. Many are false positives -- citizens mistaking a firework or car backfiring for a gun.

Contact Heather Somerville at 510-208-6413. Follow her at Twitter.com/heathersomervil.