LOUD ENOUGH: 7 extra large 1.5" metal dog doorbell and metal inner ball, make clear loud ringing sound, easily audible from other room even when dog softly touches it DOG EASY LEARN: After simple training, most dogs are able to learn to touch the bells in about one day and fully learned to hit them to go outside or potty next week LENGTH ADJUSTABLE: Two snaps design for tighten the dog training bell into different belt length, makes it universal for most doorknob height, big dog, small puppy dog STRONG BELL METAL: To avoid pup chew or bend the dog training bell apparently, avoid the small metal ball go out of the potty bells, our dog bell use super strong metal EFFICIENT COMMUNICATION: Using dog door bell have been taken as an easier, fun and a win-win way for dog to talk with you instead of barking, scratching