Koso/Pacific Seismic Products is the world's leading manufacturer of earthquake/seismically actuated gas shutoff valves. Pacific Seismic Products was formed in 1989 when it acquired the rights to Koso’s seismic valves. Today, the products continue to be produced in Lancaster, CA.

These valves contain sensing mechanisms which cause the valve to positively shutoff the flow of gas upon detecting a given peak acceleration over a period of time. These valves can only be reset manually which allows for careful inspection of the gas system prior to reset. Automatic reset mechanisms are not recommended, as they may not be sensitive enough to detect a slow gas leak.