If you want to make a room accessible only by a key you must first make an object of type key and then place that objects vnum in the exit menu. To prevent a thief from picking the lock you must also set the PICKPROOF flag. Always create a unique name and description for your key and give hints in the description about where it should be used. A good practice is to ensure keys load more than one instance since key storage in a house is no different from a character always idling with keys to hoard them. Single instance keys are a bad idea since if a player dies behind a door with the only key in their corpse they have no way to get back. Also, keys should always be the first dependent object loaded to a mob so they don't rely on other equipment loading to the mob prior to it. See also:: KEYS, ZONE-DESC, REDIT-EXIT