The fire was reported at 8:40 p.m. Tuesday at 1991 Camino Ramon Place, said Mike Brown, battalion chief of the San Ramon Valley Fire Protection District.
"Electrical stuff is part of life," Brown said. "Sometimes malfunctions happen and start fires."
The couple and daughter living in the duplex heard the smoke detector go off and saw the smoke in the bedroom. They called 911, and evacuated. Some of the neighbors also vacated their homes. No one was injured.
Three fire engines, two trucks and a paramedic unit showed up at the scene. Firefighters doused the flames and had the fire under control at 8:55 p.m.
The fire caused $20,000 worth of structural damage and $10,000 worth of furnishing damages. Firefighters did not see any problems in the adjacent apartments.
"Smoke detectors are key to getting out of the building safely," said Brown.