Why does it matter why the op wants to know and/or how anyone else parents their children? I know it's CRAZY that a child just wouldn't listen among any other things that could be going on, and that a parent would rather be pro-active in their planning. Good gravy. Answer the question and move along. No one should have to present every detail of their lives, their children, parenting styles, or individual concerns to get a question like this answered.
OP - I second the bells on the door, leaving a light on in the area for bathroom access, and even sleeping on the pull down if you're really worried about him unlocking the latch and leaving.