The Pet Sensing Doorbell.

This is the cordless doorbell that chimes only when a dog or cat wearing a "smart key" approaches, alerting you that your pet wants to be let in or out even when you're out of eyeshot. The unobtrusive smart key attaches to a pet's collar and transmits a coded signal that rings the doorbell when it comes within range (adjustable from 6" to 3'). The tone sounds for about seven seconds and repeats every 5-10 seconds. Its volume adjusts to four levels--the maximum volume of 101 decibels is as loud as a motorcycle--or the unit can be turned off. It comes with one smart key and can be used with up to five pets (additional smart keys sold below). The sturdy ABS housing mounts within 24" of the floor near the door opening, and includes a low battery indicator and a picture holder. Batteries provide power for 6-10 months; doorbell requires three C batteries, smart key uses an included RFA-67 battery. 5"H x 8 3/4" W x 2 1/4" D. (12 oz.)