PetSafe Electronic SmartDoor

Unlocks as your pet nears, re-locks automatically after pet enters or exitsFeatures 3 modes: Locked, unlocked and automatic accessActivation via SmartKey ranges from 6 inches to 3 feet and can be easily adjusted by pet ownerSmartKey conveniently fits on pet's everyday collar and only weighs .64 ouncesBattery powered – requires 4 D Cell batteries, not included