The PC Moderator is a parent without the nagging. The small device (see image) attaches to a VGA port to limit computer use. After a set amount of time, the moderator blocks signals to the monitor. Game over. It can be customized to allow different lengths of time for different users and comes with a padlock and is in a tough shell (in case of physical attempts to remove it). Lol?

California Offers Chastity Belts for WoW Addicts [GamePolitics]