County workers discovered last week that five out of eight sirens did not work.
They're supposed to provide tsunami warnings along roughly 30 miles of coastline from Pacifica to Pescadero.
County officials say repair work should be finished by early September.
Until then, extra police and sheriff's deputies will work to alert the public in the event of a disaster.
Text alerts, emails, and telephone warnings also would be used in the event of emergency.
