Neither of my dogs give crystal clear signs they need to go out (whining, barking, scratching at the door), but Millie is obvious. She demonstrates really excited behavior (play bowing, panting, running in circles) and when I get up she runs to the door and looks at me pointedly.
Fable doesn't really. She sniffs around the area where the door is, but I need to not be staring at the computer screen to notice.
Mostly I just let them both out at regular intervals.
I've seen a lot of doorbells for dogs to let you know when they have to go out. Opinions?
The ones that start out with a treat inside the bell to lure the dog into pressing it, I see a problem with Fable. I can clearly imagine the "BING! BING! BING! BING! BING!" behavior expecting treats long after they were fazed out. She's persistent that way.