Add an additional pet to your Electronic SmartDoorPet Door or replace your current SmartKey Collar Key. Our innovative Smart Door Pet Door recognises the SmartKey Collar Key worn on your pet’s collar and unlocks the pet door. After your pet has passed through and the pet door no longer senses your pet's SmartKey™ Collar Key, the pet door automatically locks back into place. Up to 5 SmartKeys™. Collar Keys can be programmed.