Dogs don't potty in places where they eat, sleep, or spend a lot of time. This is why a crate is so great for potty training, because you're pretty confident that your puppy won't potty while she's in the crate since that's where she eats, sleeps, AND spends a lot of time. As she settles in to her house, she will start to feel like it is hers and she will not want to soil it.
Dogs do potty where they have pottied before, or where they have been reinforced for pottying. If they sneak away into a room where you're not watching and potty, not only are they more likely to potty in that place again (because it smells like they've pottied there before), but they've been reinforced for pottying there (relieving themselves makes them feel better). That's why it's so important to prevent accidents and reward good behaviors.
Personally, I would not use the bell. I know several people here have used it with success, but I also know of a LOT of people whose dogs end up ringing the bell anytime they're bored and want to go outside to play, or just ring the bell for fun all day long. Plus I don't like pushy dogs. IMO, it's more effective and better for your relationship to simply learn your puppy's potty schedule and take him out when you think he needs to go out. This way he'll begin to trust you that you'll be able to take care of his needs. It's harder, though, because you will have to really remember when to take him out, but that's why humans are smarter!