It might depend on where you live. I know that when I've lived in apartments, the leasing office was to give you at least 24 hour notice before entering your apartment, BUT they did say that in the case of an emergency they were allowed to enter your apartment without notice or without you there. My sister lived at the apartment complex I'm moving to and they came into her apartment while she wasn't there because they were checking for damages since she was moving out and needed to make a list of the things they would need to repair any damages. Now, that I think should be illegal, but they did it anyway. With notice, I can easily hide or move my cats to make it seem I am complying with the rules, but without notice, I could easily get caught with too many cats.