Chess, but with a slight rule change.

My grandfather was the one who taught me how to play chess when I was younger, and sometimes we played with a little rule change. We all know that basic rules do not allow the king to put itself in check, and once placed in check, you MUST do something about it like move your king, capture the piece putting you in check, etc.

Sometimes when we played, we put in these rules.

1) The king COULD place itself into check if the player didn't see it.

2) We did not have to say check when putting our opponents king in check, and you technically didn't have to do anything about it once put in check. So if he put me in check, and I didn't see it, he could "capture" my king on his next move, ending the game.

Basically, we treated the king as a normal piece as far as being able to capture it, except for if it gets captured, the game is over.

Has anyone else played with this rule before? What are your thoughts? It certainly made the game a little more challenging for me as a kid.