5 month old pup - peeing inside

For the most part, my puppy seems to be getting better about not peeing in the house, but when he does have an accident, he does not tell me that he has to go and just pees. I've tied bells to the front door and ring them every time we go out so he knows that to go out you have to ring the bell, but he won't do it on his own.

He also "tinkles" when he gets really excited - when he meets new people, when I come home, etc.