Recently I was home with the children. We were in the master bath/bedroom, with the door to the rest of the house shut. We'd each taken a turn in the bathtub and were on the bed in various states of undress (is it counted as undress if it's pajamas and a robe?), having a very casual evening, watching a cartoon when I heard what sounded like a car door. I peaked out the window and saw MIL and Step-FIL driving away from our home. Shocked, as there had been no knock or "hello" that I had heard, I called DH, who called them. They had stopped by for a visit, come into the house, realized the kids and I were shut in the bedroom and decided to peacefully leave rather than bother us.
MIL has since been very good about calling first. I was just grateful they hadn't let themselves into the bedroom.