[FirstYorkie]

We use a bell suspended from the back door, like Erin suggested. Works wonderfully well for us!

Jodie is also right that most dogs will eventually figure out a way to let you know when they have to go (I just happen to prefer the bell-ringing method). I had one dog and a cat who would just sit and stare at the back door when they needed to go. I had one dog who would come to me and spin in circles. I had one Husky who would "talk" to me and run excitedly back and forth between me and the back door. They do figure out a way to communicate with you eventually, but it takes time (and perceptiveness on your part!).