Legal Question in Real Estate Law in California

There is no law against it, but it is probably a violation of your lease and could be used as grounds for eviction. A landlord has responsibilities for the property even after they turn posession over to you. Sometimes that may require them to enter the premises without notice in case of emergency. So they have a right to keys to any locks on the premises. If you have a problem with your landlord entering without 24hrs notice or outside the hours of 9a-6p, Mon-Sat, you have legal rights and remedies to stop that, but changing the locks is not one of them.

I agree. The law does not encourage or support self-help of this kind. Stick to your legal rights and remedies. Keep in mind that the landlord is prohibited from re-keying the property as a means of self-help eviction. Similarly, you should not interfere with the landlord's right to enter without notice in the event of an emergency.