In California a guest has a reasonable expectation of privacy subject to certain limitations.  A court will find that there is a violation of a guest's right to privacy if: (1) the guest has a legally protected privacy interest (2) a reasonable expectation of privacy and (3) conduct by defendant that amounts to a serious invasion of the protected interest. 
 The answer is that the Innkeeper has a limited right to enter the room for at least the following reasons: to protect and ensure the safety of any guest, the innkeeper suspects potential illegal activity (but do not let police in without a warrant), and after check-out time there is small or no expectation of privacy.