The small Electronic PetSafe Smart Door grants your dog exclusive access to your home with a PetSafe’s award-winning SmartKey dog door tag, located on your dog’s collar. After your dog has passed through the electronic dog door, the dog door automatically locks. PetSafe Smart Door Features:Adjustable SmartKey sensing range up to three feet away Plexiglas dog flap, which locks in both directions Smart Door system can identify up to five SmartKeys per household Three easy-to-set pet entry modes: locked, unlocked, and automatic Energy efficient, weather-resistant insulated dog door flap and seal Uses 4 D-cell batteries (not included) Fits door thickness 1 1/2″ to 2″ Perfect for dogs weighing up to 15 lbs Optional dog door installation kitSmart Door Dog Door Dimensions:Dog Door Exterior Size - 17 3/8″ x 25″ Dog Door Flap - 13 1/16″ x 15 3/4″