Say goodbye to the scratching, whining, and barking when your best friend needs to visit the backyard. You’ll stop waiting in the doorway, impatient for his return. PetSafe's Smart Pet Doorbell has an audible tone that tells you he’s ready. A must-have for busy homes. Alerts you when your pets need in or out. Detects your pet's Smartkey® from inside and out. Mounts securely on door, wall, or glass. Adjustable detection range up to 15 feet. Personalize it with your favorite pet photo. Adjustable volume levels. Low battery indicator. Recognizes up to 5 pets. Requires 3 “C” batteries (not included). Lifetime Limited Warranty.