Advanced Locks and Traps (CTH)

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The game works perfectly well under the assumption that a lock is a lock, regardless of its make or mechanism. Traps generally earn greater detail ("a poison needle flicks out of the panel beside the lock," for example), but even so, the actual workings of the device are not usually described.
However, locks and traps are in fact found in great variety, and while many might provide little challenge to the skilled thief, some will prove daunting even to the most experienced veteran. A device can be listed with a modifier of + or - up to 30%, reflecting the ease or difficulty with which a thief might pick the lock or find and remove a trap. The modifier is applied to the thief's chance of success with the obstacle; a –30 lock, for example, lowers the thief's chances of picking it by 30%. If his normal percentage is 65%, then his chance with this lock is only 35%.
==Modifying Checks==
The major considerations for determining the difficulty of a trap are the skill of the locksmith or trap maker, the materials used for the job, and the purpose of the lock or trap. Some examples for locks are listed:
+15%	Typical latch on small house, guest room of an inn, storage closet, etc.
0 	Lock on a merchant's house, weapons locker, wine cellar of a large inn, etc.
–15%	Door to a cell or keep, security checkpoint within a dungeon, lock on a gem cutter's shop or moneychanger's house.
-30%	Lock on a major vault or most intricately designed cell door
These guidelines should be used by the DM to establish a variety of challenges in the campaign setting. The many varieties of traps are too great to list, but the same principle of modification applies.
The new equipment listed in Chapter 5 includes a variety of aids for just such delicate work. By utilizing greater detail in the description of a lock or trap, more opportunities for the use of this equipment will arise.
==Building Better Locks==
A character with locksmith proficiency can try to build a superior lock, but only if the proper materials are available. In most cases this means an iron or steel lock, though special considerations can be adjudicated by the DM. The locksmith must make a proficiency check for the lock. A roll of 1 or less indicates a lock of superior craftsmanship. Subtract 1 from the die roll for every proficiency slot beyond the first spent on the locksmith skill. For example, a craftsman with three slots of locksmith skill creates a superior lock on a roll of 1, 2, or 3.
The modification for such a specific lock is determined by rolling 1d10, resulting in a 1-10% modifier. Each improved lock will be at least as good as the one before it, however, so re-roll results that are lower than the modifier for a previous lock made by that same smith. When the locksmith makes locks with a 10% modifier, he is allowed to roll 2d10. When he reaches 20%, he receives 3d10, but is no longer guaranteed to beat his previous high roll. He does get to roll 3d10 until he gets a result of 20 or greater, however.
For example, a locksmith builds a superior lock and rolls a 7% modifier. On his next superior lock, he rolls and discards a 6, 3, and 5, before rolling a 10. He keeps the 10, since that is the first roll to equal or beat his previous high of 7. On his next superior lock, he rolls 2d10, using the first adjusted roll of 10 or higher. If he eventually gets a 20, he rolls 3d10 until he gets a result of 20 or greater. All his subsequent superior locks, then, will gain at least 20% modifiers, with the occasional one perhaps as high as 30%.
==Multiple Locks==
A simpler way to make a room or chest more secure against thieves is simply to protect it with more than one lock. Iron-bound chests with two or three built-in locks were not uncommon in rich treasure vaults. Certainly a powerful and suspicious wizard would not entrust his spellbooks to a cabinet with only a single lock.
==Lockpicking/Trap Removing Noise==
A thief attempting to open a lock or remove a trap with complete stealth can try to do so. He suffers a -10% chance to his ability rating, but will perform the task quietly on any roll except 01-10%. In the latter case the lock or trap makes a sharp click, snap, or other sound, audible to anyone within earshot.
If a thief fails a silent attempt, he cannot try to open the same lock normally.