I rented out a room to someone in my condo that I also resided in, in California. She vacated one night at 1:30 in the morning, but did not give written notice or return the keys. She also stole my car that night on her way out (but that's a separate issue to the security deposit and she did leave it on the street out front a week later, she was likely on drugs). About 2 weeks later I did get the keys back from her mother who came down from England to visit her daughter/my ex tenant in the psych ward. I do not have a forwarding address for my ex tenant, other than her mother's address in England, although she does not live with her mother. After 30 days from not hearing from her she called me on the phone to ask for her deposit. Granted it doesn't feel right to return her deposit after the hell she put me through, but I don't want to do anything that could give her reason to sue me. My question is this, it states in writing on the month to month tenancy agreement that she must give 30 days "written notice," but she did not give any written notice, and she didn't return the keys until two weeks later. Does not giving written notice forfeit her deposit? Or do I still return the deposit prorating the days until when I received the keys back? Or is it from the date she left despite not having the keys returned? A bit confused on this particular situation.

If she did not cause any damage to the property, and if she did not owe any rent when she left, then you are not entitled to retain the deposit.

The time for returning the deposit begins when possession of the property is turned over to you. You could probably argue successfully in court that the time began when she returned the keys to you. Since she had the keys during those two weeks, technically she owes rent for those two weeks. So if she did not previously pay for that time then the most you could retain from the deposit would be two weeks worth of rent.

{personal attack removed-<>}
Your lease agreement states clearly the tenant should give a 30 day notice, your psycho roommate signed that before she moved in!
Now not only did she break the rules by not giving you proper notice, she also kept the keys to the property!
You have all the right to keep the deposit + sue her for the cost of replacing the locks + the money you lost by not being able to rent your apartment! I'm pretty she didn't clean the room either so that's another charge to think about if you really want to get technical.
You are absolutely entitled to that money, you lost business and she exposed you to a dangerous situation by not returning your keys.

First, you join this site today and the first thing you do is attack one of the more respected people here and without any basis. Plus you do so on a thread more than three months old.

Lisa's answer was correct. What Lisa said was if the tenant does not owe any money then the landlord is not entitled to keep the deposit. That answer is legally correct.

The question is, therefore, whether the tenant owed any money. Since the tenant did not follow the lease by giving 30 days written notice, then the landlord can charge her for rent for 30 days from the notice, or if there is no notice then 30 days from retaking possession of the partment.

Now there are two more provisos here. CA law requires that the landlord send the tenant an accounting of how the deposit was used and any balance within a set time (I believe its 21 days in CA). If the landlord does NOT do so the landlord forfeits the right to keep ANY of the deposit.

As for charging rental for 30 days from taking possession, CA law requires the landlord try to mitigate damages. This means that if they find a new tenant within the 30 days, they can't collect rent from the former tenatn once they have a new one.