Can your landlord unlock your door for the police to enter when they do not have a search warrant?

Whether or not a search warrant is required depends on the facts of the case.  If this was an emergency situation, the police would not need a search warrant.  If contraband was in plain view such as sitting near a window, the police would not need a warrant.  The police would not need a warrant for contraband in plain view because by the time they obtained a search warrant and returned, the contraband might be gone.  Also, with regard to the emergency situation (exigent circumstances), the emergency could endanger health or safety by the time the police obtain a warrant and return.

Another issue presented here is consent.  Since the landlord is the owner of the property, the landlord might be able to argue that he or she has the authority to consent to the police entering your apartment.  As a tenant, you may be able to challenge the validity of the consent given by the landlord.  If the police had not been there, the landlord could enter your apartment in an emergency without prior notice.  If it is not an emergency, the landlord has to provide the tenant with notice prior to entering the apartment.  The amount of advance notice varies from state to state.