Most written rental agreements for residential tenancy expressly preclude the tenant from making any alterations, additions, and modifications without the written consent of the owner. If your tenant violates this provision, your alternatives are to (1) request that the tenant restore the original locks, or provide you with keys to the new locks, or, (2) prepare and serve a "Three Day Notice to Perform Covenant or Quit" upon the tenant, and if the tenant remains in possession and refuses to provide you with the keys or restore the original locks, file a lawsuit for Unlawful Detainer to have the tenant evicted from the rental, or (3) if you have a month to month tenancy, serve the tenant with a "Thirty Day Notice to Vacate" [since January 1, 2003 however, if the tenant has resided in the residential tenancy unit for one year or longer, you must serve a Sixty day notice to vacate rather than a thirty day notice to vacate.] If your tenant fails to vacate, you should then file a lawsuit for Unlawful Detainer to have the tenant evicted.

See the new law that went into effect on 1/1/03 regarding the issuance of either a thirty day notice to vacate or a sixty day notice to vacate: California Civil Code Section 1946 and 1946.1: A hiring of real property, for a term not specified by the parties, is deemed to be renewed as stated in Section 1945, at the end of the term implied by law unless one of the parties gives written notice to the other of his intention to terminate the same, at least as long before the expiration thereof as the term of the hiring itself, not exceeding 30 days; provided, however, that as to tenancies from month to month either of the parties may terminate the same by giving at least 30 days' written notice thereof at any time and the rent shall be due and payable to and including the date of termination. It shall be competent for the parties to provide by an agreement at the time such tenancy is created that a notice of the intention to terminate the same may be given at any time not less than seven days before the expiration of the term thereof. The notice herein required shall be given in the manner prescribed in Section 1162 of the Code of Civil Procedure or by sending a copy by certified or registered mail addressed to the other party. In addition, the lessee may give such notice by sending a copy by certified or registered mail addressed to the agent of the lessor to whom the lessee has paid the rent for the month prior to the date of such notice or by delivering a copy to the agent personally.

1946.1. (a) Notwithstanding Section 1946, a hiring of residential real property for a term not specified by the parties, is deemed to be renewed as stated in Section 1945, at the end of the term implied by law unless one of the parties gives written notice to the other of his or her intention to terminate the tenancy, as provided in this section. (b) An owner of a residential dwelling giving notice pursuant to this section shall give notice at least 60 days prior to the proposed date of termination. A tenant giving notice pursuant to this section shall give notice for a period at least as long as the term of the periodic tenancy prior to the proposed date of termination. (c) Notwithstanding subdivision (b), an owner of a residential dwelling giving notice pursuant to this section shall give notice at least 30 days prior to the proposed date of termination if the tenant has resided in the dwelling for less than one year. (d) Notwithstanding subdivision (b), an owner of a residential dwelling giving notice pursuant to this section shall give notice at least 30 days prior to the proposed date of termination if all of the following are true: (1) The dwelling or unit is alienable separate from the title to any other dwelling unit. (2) The owner has contracted to sell the dwelling or unit to a bona fide purchaser for value, and has established an escrow with a licensed escrow agent, as defined in Sections 17004 and 17200 of the Financial Code, or a licensed real estate broker, as defined in Section 10131 of the Business and Professions Code. (3) The purchaser is a natural person or persons. (4) The notice is given no more than 120 days after the escrow has been established. (5) Notice was not previously given to the tenant pursuant to this section. (6) The purchaser in good faith intends to reside in the property for at least one full year after the termination of the tenancy. (e) The notices required by this section shall be given in the manner prescribed in Section 1162 of the Code of Civil Procedure or by sending a copy by certified or registered mail. (f) This section may not be construed to affect the authority of a public entity that otherwise exists to regulate or monitor the basis for eviction. (g) This section shall remain in effect only until January 1, 2006, and as of that date is repealed, unless a later enacted statute, that is enacted before January 1, 2006, deletes or extends that date.