Custom K9 Design endorses "Pavlov's Housebreaking Method"! Successfully training your puppy to ring a bell at the door to indicate a need to go outside is easy, quick and effective. Read more about using this method HERE. The Pro Door Ringer consists of 4 sleigh bells fastened in-line down the leather strap. Instead of providing a piece of shoestring leather to tie around the door knob, we prefer a more substantial 3" diameter metal ring, which slips easily over most door knobs. This is both more durable and more visually appealing. There is a buckle for height adjustment, so that you can set it appropriate to your dog's height. This feature is unique in the industry, and is perfect for growing puppies! The Pro Door Ringer leather is available in Black on Black, Chestnut on Black or Tan on Black, and the hardware/bells are available in silver or gold.