We have had Wrigley for a week today

Well he is doing well on potty training as far as going outside. When we take him outside to go he does either pee or poop when we take him out. Normally rather quickly after we got outside even, so he knows that is why we are out there. We take him to the same spot when we want him to simply go and when he does we praise him and bring him immediately back inside so he knows he did what he was suppose to do. We also take him other places like for walks and he goes to the bathroom on those walks too so that he doesn't think the only place to go outside is in the one spot we take him if that makes since.
So here is my issue. He knows how to go outside and does it well (meaning he does his business then expects praise and wants to go back inside afterwards) BUT he doesn't seem to destinguish between going outside and going inside.
I *think* the problem is he doesn't know how to let us know he needs to go. He sniffs around constantly even if he doesn't have to go, maybe he is still getting used to living here I don't know so we can't really just watch for that. I've heard some people use a bell on the door, does that seem to work? The only thing is he doesn't even go near the door, he just lets loose wherever he is.
So how do I help him let us know when he needs to go out? Any other methods than the bell method? I will try it if it might work, but I have a bell I have a feeling he would just go over and play with it all of the time.