The court doesn't hand out a free win
It's a common assumption: the other side skips the hearing, so the plaintiff wins by default. That's not how California small claims court works. Under Code of Civil Procedure § 116.520(b), if the defendant fails to appear, the judge still has to require the plaintiff to present evidence and prove the claim. The plaintiff generally still has to show up, explain what happened, and back it up, a contract, an invoice, photos, texts, whatever supports the amount being asked for. The judge listens to that, then rules based on what's actually presented, not on the fact that only one side bothered to appear.
In practice this means the hearing is short. There's no one to cross-examine, no argument to rebut. But the plaintiff's burden doesn't disappear just because it's uncontested.
Proof of service has to be filed first
Before a judge will do anything about an absent defendant, the court needs to see that the defendant was actually and properly served with the claim. That's the Proof of Service (Small Claims), form SC-104, and it generally has to be filed with the court in advance of the hearing date, not brought along on the day. No proof of service on file, or one that's filled out incorrectly, and the judge can't proceed on that defendant at all. The hearing gets continued, or service has to happen again, before the case can move forward.
What happens if it's the plaintiff who doesn't show up
The rule runs the other direction too, and the outcome is different. If the plaintiff is the one who doesn't appear, the court doesn't decide the case on the merits, because there's no one there to present it. The case is generally dismissed instead (Code Civ. Proc. § 581(l)), usually without prejudice, which means the plaintiff can typically file again. A no-show plaintiff doesn't lose the underlying claim the way a defendant risks losing by staying home, they just lose that hearing date.
If a defendant missed the hearing and lost
A defendant who didn't appear and had judgment entered against them isn't stuck with it automatically. California lets that defendant file a motion to vacate the judgment, on Judicial Council form SC-135, with the clerk of the small claims court. Under Code of Civil Procedure § 116.730, that motion generally has to be filed within 30 days after the clerk mails the Notice of Entry of Judgment (form SC-130) to the parties.
Filing the motion isn't enough by itself. The court is looking for good cause for missing the hearing itself, things like excusable neglect, a mistake, or genuine surprise, not a general belief that the judge got the outcome wrong. Disagreeing with how the case was decided isn't the same as having a reason for not being there to decide it.
There's a separate track for a narrower situation: a defendant who was never properly served in the first place and only found out about the judgment later. Under Code of Civil Procedure § 116.740, that defendant generally has up to 180 days from discovering the judgment to file the same kind of motion, longer than the standard 30-day window, because the problem there is that they never had fair notice of the case to begin with.