Duke is that way, once Adam or I go to the door and let them in he is fine. Our cable guy came yesterday and he barked/growled until Adam let him in and then he was happy and normal. He will bark until he knows it is ok. If we don't go to the door he will continue until the person is gone. He isn't aggressive towards the person when we let them in, just a warning I think, an alarm to let us know someone is there.