Otis Aut-O-Safe is an elevator emergency return unit, used on most currently made Otis hydraulic elevators. The unit has a battery in it. If the power goes out, the battery powers the elevator, so the elevator can move. Then, the elevator goes down to the lowest landing, and will not go back up again. The doors will open, then passengers can exit. The doors then close. The door open button in the elevator is still enabled so no passengers get trapped in the elevator. This emergency return unit was made from around 1990-present.