[jaak]

Not a lawyer and not in California.

As others have pointed out, most companies don't care about misdemeanors. And, technically you were arrested when you turned yourself in - at that moment you were not "free to walk away" even if you weren't physically taken into custody.

The company I work for (multi-state) does national criminal background checks on every employee. It's been my experience that if you have a record it'll probably come up (sealed or not). The reliable background check companies have multiple sources and odds are probably pretty good your history will be in some database. I would assume whatever you did is going to show up, at least partially.

If they ask, be honest. If they don't ask, don't tell. At larger companies the recruiters will know very well what they can and can't ask (asking the wrong questions can result in an expensive lawsuit), so they will be very careful about that.

At my company lying about a criminal background is not automatic grounds to dismiss a candidate (we will still take into consideration the circumstances, nature of the crime, and length of time since release from supervision), but it will not impress the hiring manager if you are caught lying.