The Petsafe Electronic Smart Door and Passport Smart System Pet Doors come standard with one collar key but both systems can be expanded to allow you to control the access of multiple pets (with the purchase of additional collar keys). The Smart Door can be expanded up to 5 pets and the Passport Door can be expanded up to 20 pets! Only pets wearing the SmartKey or Passport Key on their collar can pass through the electronic collar-activated dog door.
These doors use radio frequency technology to operate. Pets wear a collar key sensor that triggers the door to unlock. After your pet passes through it automatically re-locks.