According to a California site:
8. CAN MY LANDLORD ENTER MY APARTMENT WITHOUT MY PERMISSION?
You have a basic right of privacy which your landlord should
respect. Your landlord may enter your place only in the following
cases:
-- in an emergency.
-- to make necessary or agreed upon repairs, decorations,
alterations or improvements; supply necessary or agreed
upon services; or show the unit to prospective buyers, tenants
or repair workers.
-- when you have abandoned or given up the premises.
-- as a result of a court order. (Sec. 1954 of CC)
Unless it is an emergency or impractical, your landlord should
give you reasonable notice of his/her plans to enter, and enter only
during normal business hours. Twenty-four hours is usually
considered reasonable notice.
If your landlord seriously violates your right to privacy, you
may have the basis for a lawsuit. You also might want to contact the
police when the violation occurs; while the police often will not take
direct action, your report to them can help document your complaint
if you take the case to court.
http://www.tenant.net/Other_Areas/Calif/misc/tenant.html
It also answers these questions:
Lease and Rental Agreements (Questions and Answers)
1. Can I Get My Deposit Back?
2. Can I Get Money Back To Hold A Rental?
3. How Much Notice Do I Have To Give?
4. If Repairs Are Needed, What Should I Do?
5. Can I Be Forced To Move?
-- The Eviction Process
-- Retaliatory Eviction
6. Can My Rent Be Raised?
7. Can I Get Interest On My Deposit?
8. Can My Landlord Enter My Apartment Without My
Permission?
9. Can I Sublet My Apartment To Another Tenant?
10. For More Information