We installed a doggie door in a sliding patio door in the bedroom. It works great—a great investment but my daughter said that she has a friend that has a puppy and they taught the puppy to ring a bell that is attached to their door with a suction cup. The pup is quite young and yet lets them know when the pup needs to go out.
We have so many critters out here I'd be afraid of what might find it's way into our home.
I wish I could do that though.