If you think you’ve seen everything, I’ve got something for you. Check out the Smart Chime – Wireless Pet Doorbell. Too, too clever and too, too cute.
From the Web Site:
You don’t need to stand around and wait while your pet goes outside. The Smart Chime is a wireless doorbell that your pet can easily be taught to use to let you know when he’s ready to come back inside. You can also place the doorbell trigger inside for your pet to tell you when he needs to go out. The kit even comes with a standard door chime that your visitors can use, as well. The interior door chime is powered by three AA batteries; the pet switch requires a 9-volt battery, and the door switch is powered by a 12-volt 23A battery. Batteries are all sold separately.
Select Dog or Cat to hear barking or meowing when the chime is triggered. The Smart Chime has a 100-foot range, so you’ll be able to place the interior door chime in a convenient location.
All mounting hardware is included in the kit. Pets can be trained to use their paws or noses to activate the wireless doorbell. Some pets may require more training than others, but using treats as rewards, you should be able to teach your pet to use the Smart Chime system in a week or two.