When the Do Not Disturb Sign Doesn't Work

If locking the door sends the wrong message and the “Do not disturb” sign doesn't work, now there's a third option: disappear the doorknob. This smartly designed doorknob by Arnaud Lapierre is one of those “why didn't I think of that” moments. You can't make the whole door disappear (or the kids) so why not the knob.