It's called an elevator

Watching The Big Bang Theory last night (my current favourite), the scene in which Sheldon and Penny are having a conversation as they walk the numerous flights of stairs to their apartments. On each landing they pass the elevator doors, criss-crossed with 'Out of Order' tape. In the ad break 9 Year Old Boy turns to me and asks "Mummy, why are so many of those rooms out of order?".