The eight sirens are scattered up and down the coast, and while not loud enough to make people cover their ears, the tests sirens were at full blast.
This was the first time the sirens had been tested at full volume. Crews have been working on the warning system for the past three years.
Some residents say the county needs to do more outreach about the new system and it still needs a couple of tweaks.
"I've heard it before," fisherman Joe Robertson said. "I work in Princeton sometimes and it's really, really loud there, almost unbearable, but here it's not so bad."
"I didn't know what it's about," fisherman Greg Mariano said. "I heard it; everybody heard it, but I had no idea what it was about."
"We've put out to the press over the past couple of weeks that this was happening, so we're hoping there'll be no panic," San Mateo County Sheriff's Lt. Ray Lunny said. "Then, next year as we start rolling this out and doing it on the first Wednesday of the month, I think people will get used to it."
In a real tsunami warning, the sirens will be sounded continuously for several minutes. An automated telephone call will also go out to residents.