I may have inadvertantly done this w/ my last litter. I have a brass bell that I hang in the expen-- not intended for any other reason but to make NOISE (I try to desensitize to all kinds of noises)! One of the pups supposedly already "figured it out" that if he rang the bell hanging on their door (the bell was right next to the potty pool this last time!), he could go out....

IMO, this is a recipe for a lot of owner exercise.

Been thre, done that.

Teach the dog to ring the bell, either with her nose or her paw. Click/reward when she does it. When she can do it reliably you can name it "ring the bell". I have a bell that I tie to the bottom rung of a chair that sits near the door. Every time we go out for a potty break, I ask the dog to ring the bell. The dog soon catches on. She doesn't overly ring it, but sometimes uses it to tell me that it's time for supper, a walk, or that I forgot her suppertime cookie!

We also have an "Easy" button from Staples. Lots of fun, same idea, except these can be picked up, chewed and physically abused........

I bought leather string/cord from Michaels and about 8-10 large bells for each door. Made the stands myself.

My problem is my youngest pup rings it and the 9 month old stopped ringing it so we are re-training him to ring the bell. We bang their paw or nose on it.