Petsafe SmartDoor Electronic SmartKeyPetsafe SmartDoor Electronic SmartKey Replace a SmartKey or add more pets to your PetSafe Electronic SmartDoor. The SmartKey fits most collar ID tags and uses RFID technology to send a signal that locks and unlocks the door flap when it senses your pet. You can add up to 5 pets to your SmartDoor. Package includes 1 SmartKey and 1 battery (RFA 67). Key Benefits: Unlocks Door for Your Pet The SmartKey lets your pet come and go; fits most collar ID tags