Landlord/Tenant Question about keys

[Amy T.]

CA laws state that keys must be returned to the landlord or the landlord can have the locks re-keyed and deduct the expense from the deposit. This is obviously a safety issue for future renters so that no one has access to their home. But how do we know that copies weren't made and being held on to?
Do you always re-key a property when you turn it over?