D.W.
We put one of those child locks on the inside knob of his room. That way he can't get out but we can still get in quickly to get him. Other people put up gates. Basically I treated it like when he was learning to sleep the whole night in his crib on his own. We let him cry it out a little and then go in and lay down next to him for a bit then let him cry it out for a bit then lay down with him. After about a week he got it. He actually didn't really cry at all - he yelled a little but he wasn't crying. Sometimes he'll play on his own for a bit in his room before he lays down and takes a nap. That's fine with me too- it actually extends his naptime some.