Before you let them find out or tell them or whatever. Make sure your doing good in school. That seems to be the #1 concern with parents. If you're making straight A's, they're likely to take it easier on you. But it is THEIR house and if you want them to know you smoke, then know that if they don't want an illegal drug in their house..then you should respect that.

My parents don't seem to care that I smoke as long as I don't do it around them or at home. (Which seems odd..I'd rather have my kid smoking next to me then out somewhere doing god knows what)