I have 4 daughters (grown now). When they were little and I wanted to sew and have some "me time", I would wear an old dixie cup sailor's hat. When the hat was on, they were trained to think I was invisible and could only talk to me if there was an emergency. Most of the time they would run in and say: "Oh, mom has the hat on." There was one time though one's comment was: "Mom, I think this is an emergency- Kimmy cut her thumb off." They are all in their late 30's/early 40's and still talk about that hat.