PetSafe Electronic SmartDoor, Automatic Dog and Cat Door, Collar Activated with SmartKey, Small or Large CUSTOMIZE YOUR PETS ACCESS: The SmartDoor features programmable selective entry, exit and auto-locking options PEACE OF MIND: The SmartDoor works with the waterproof SmartKey worn on your pet's collar; only the pets wearing the SmartKey can go in and out MULTIPLE PETS: Great for households with multiple pets; programmable for up to 5 SmartKeys BATTERY OPERATED: The SmartDoor is battery operated (4 D-Cell Batteries, not included) DOOR INSTALLATION: Designed for installation in interior/exterior doors; wall installation option available with purchase of Wall Install Kit PRODUCT SUPPORT: PetSafe brand's U.S.-based Customer Care experts will be glad to help; call Monday through Saturday at 1-800-845-3274 EXPERIENCE: PetSafe brand has been an industry leading U.S. manufacturer of pet behavior, containment and lifestyle products since 1991, helping millions of people and pets each year