When to notify family

When did you tell your family you were in labor. As soon as you checked into the hospital? When you were a certain number of centimeters? I'm not sure exactly what I want to do, because I don't want people to show up at the hospital until after the baby is born, however I don't want them to know that I waited so long to to tell them he was on his way.
I'm thinking if I let the in-laws know too early, they might show up, and even though the staff won't let them in the room against my wishes, it would make me nervous to know people are sitting around waiting for me. I just want peace.