1. Tie one bell on the inside of the door and one bell on the outside of the door, both at the level of your dog’s nose.
2. Encourage your dog to nudge the bell with her nose by holding a food treat next to it and telling her, “Ring the bell.”
3. Each time she touches the bell, she gets a treat; if she makes the bell ring, she gets several.
4. As soon as she rings, give her the treats, tell her “outside,” and open the door. Have a helper waiting outdoors with a treat or toy. (If you don’t have a helper, you can also leave a treat or toy outside for your dog to find.)
5. The helper repeats the process, using treats to lure the dog to ring the bell, rewarding her and telling her, “Inside,” then opening the door.
Repeat this routine a few dozen times. Once your dog’s got the picture, food treats are no longer needed–being allowed to come and go at will is enough of a reward.