Cal. Civ. Code § 26

Section 26. (a) For purposes of this section, the term ''household member'' shall mean a person residing with the tenant or co-tenant as an authorized occupant of the premises, and who is 18 years of age or older or an emancipated minor.

(b) An owner shall, upon the request of a tenant, co-tenant or a household member, change the locks of the individual dwelling unit in which the tenant, co-tenant or household member lives if the tenant, co-tenant or household member reasonably believes that the tenant, co-tenant or household member is under an imminent threat of domestic violence, rape, sexual assault or stalking at the premises. An owner shall have the right to request, in good faith, proof of the status as a victim of domestic violence, rape, sexual assault or stalking, including the name of the perpetrator, if known, as provided in subsection (e) of section 24.

(c) If the threat of domestic violence, rape, sexual assault or stalking is posed by a person who is a tenant, co-tenant or household member, the owner may change the locks and deny a key to the alleged perpetrator upon receipt of a request to change the locks; provided, however, that such request shall be accompanied by: (i) a copy of a valid protective order issued under chapter 209A or chapter 258E issued against a tenant, co-tenant or household member; or (ii) a record from a federal, state or local court or law enforcement, indicating that a tenant, co-tenant or household member thereof poses an imminent threat of domestic violence, rape, sexual assault or stalking.

(d) An owner who has received notice of a request for change of locks under this section shall, within 2 business days, make a good faith effort to change the locks or give the tenant, co-tenant or household member permission to change the locks. If the owner changes the locks, the owner shall make a good faith effort to give a key to the new locks to the tenant, co-tenant or household member requesting the lock change as soon as possible, but within the same 2 business day period. An owner may charge a fee for the expense of changing the locks. The fee shall not exceed the reasonable price customarily charged for changing such locks in that community.

(e) If an owner fails to change the locks after receipt of a request under this section within 2 business days, the tenant, co-tenant or household member may change the locks without the owner's permission. If the rental agreement requires that the owner retain a key to the leased residential premises and if a tenant, co-tenant or household member changes the locks, the tenant, co-tenant or household member shall make a good faith effort to provide a key to the new locks to the owner within 2 business days of the locks being changed. If a tenant, co-tenant or household member changes the locks without the owner's permission, such person shall change the locks in a workmanlike manner with locks of similar or better quality than the original locks. An owner may replace a lock installed by the tenant, co-tenant or household member, or seek reimbursement for additional costs incurred, if the owner believes that the locks were not of equal or better quality or were not installed properly, and such action shall be deemed not to be in retaliation.

(f) If the locks are changed under this section, a tenant, co-tenant or household member shall not voluntarily give the new key to the perpetrator. An owner who refuses to provide a key to any person based on the reasonable belief that such person is the perpetrator of alleged domestic violence, rape, sexual assault or stalking, shall not be liable for such refusal.

(g) An owner who takes action to prevent the tenant, co-tenant or household member who has complied with subsection (b) from changing the locks, or any owner who changes the locks but fails to make a good faith effort to provide a key to the tenant, co-tenant or household member requesting the lock change as provided in subsection (d), shall be liable for actual and consequential damages or 3 months' rent, whichever is greater, and the costs of the action, including reasonable attorneys' fees, all of which may be applied in setoff or recoupment against any claim for rent owed or owing for use and occupancy. Damages shall not be imposed if the court determines that the owner acted in good faith.