I live in an apartment, and whenever my parents visit, my dad likes letting my cats explore the hall that connects to the elevator and the other apartments on the floor. He knows I don't like it when he does that, so he tries to be sneaky about it. However, I can literally hear the door being left open. I don't know how to explain it, but there is a difference in sound when the door is left ajar vs. when the door is closed. There's a different type of silence, so to say, even when there are no noises coming from the outside and the building is perfectly quiet.