The PetSafe Electronic Pet SmartDoor gives your pet a key to the house so he can come and go as he pleases. Using radio-frequency technology, the SmartDoor reads the unique signal of a SmartKey worn on your pet's collar and triggers the battery power-driven flap to unlock. When the SmartDoor no longer senses your pet's SmartKey, the flap automatically locks back into place. The SmartDoor can detect up to five programmed SmartKeys and also operates in two other modes: fully locked mode and unlocked mode. Locked mode does not allow entry or exit for any pet and unlocked mode allows entry and exit for all pets.