Number Locks are one of the more heavily guarded locks, as they were used to get into areas not meant for the general public. When the player comes across one, it is locked and needs a code to open it. The codes can usually be found in audio diaries or written somewhere in Rapture. Most codes are given before encountering a safe, but some are given as far ahead as four levels into the game from where the lock was first encountered. Once opened, these locks provide access to rooms and areas with various loot or hidden items.