CA law requires the landlord to give reasonable notice (24 hours is reasonable) before entering unless it is an emergency. Landlord can enter to make repairs, perform inspection, and show property to prospective purchasers or tenants if your lease is coming to an end.
Every other day sounds like too much. Maybe landlord is lonely. You are within your rights to refuse entry, but there is a fine line between standing on rights and getting landlord mad at you.
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