Kacee will be 5 months old September 9th and she was housebroken by 4 months. We bought a doorbell which hangs from the door knob and she jumps up, rings her bell and sometimes barks or makes some sort of "funny" noise. There is always someone home with her, too. We keep pads down in case no one can make it to the door in time. She might use them once or twice a week, if that often. I plan to always leave pads down for her so that they will be available if everyone is gone. Over the weekend, she needed to go potty and I don't know what brought this about but she came running into the bedroom and led me back to the door at a run.
That is the way my little Muffin used to tell us she wanted out.