Give your dog a little extra freedom with the innovative PetSafe Electronic SmartDoor Key. 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, reducing the risk of letting in strays or other unwanted animals. With three programmable modes: locked, unlocked and automatic (access only for pets wearing a SmartKey). SmartKey uses a 6v lithium battery. SmartDoor is programmable for up to five pets (additional SmartKeys sold separately). SmartDoor uses four D-cell batteries (not included). Imported.