Replace an Electronic Pet Door Key or add more pets to your PetSafe® Electronic Pet Door. The Electronic Pet Door Key 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 Electronic Pet Door. Package includes 1 Electronic Pet Door Key and 1 battery (RFA-67). Trust PetSafe® to help keep your pet healthy, safe and happy.