We learned this trick a few dogs ago, where you hang a bell on the doorknob and ring it when you let the dog out. Eventually they learn to ring the bell whenever they have to go out. It is a great house training tool.
Not so with Esme. We've had the bell on the door from day one and she still won't tell us that she has to go out. That said, she is doing ok with the house training, but it's only because we let her out at regular intervals--it's never because she asks to go out.
Interestingly, at the office, she rings the bell all of the time. But, it's not because she has to go out, it's because she wants to (either because Brian is outside talking to someone or because it's nice out). Dogs.