Masterthief

Lots of great discussion and synergistic ideas are clicking around the osr about lock picking and trap disarmament. So far:
Rather Gamey
Telecanter
Zak Smith
Roger the GS
-C

One thing that occurred to me was the similarity between some of these procedures and playing an old game of Mastermind. Every time I played Mastermind with my dad, he won. He always won chess too. Smartest person I ever met :)

Mastermind Info at Wikipedia

So, to use Mastermind for picking locks or disarming traps, it's pretty easy to vary the difficulty. You don't have to use all four slots. The fewer slots used, the easier the lock. Also, you don't have to use all the colours. The fewer colours used, the easier the lock, although I would suggest a minimum of 3 colours. The third way to adjust the difficulty is by limiting how many guesses (how many turns) are allowed before the thief fails the attempt. Failure meaning, of course, either jamming the lock or setting off the trap.

The only thing remaining for this method, then, is to assign some appropriate terms to the different elements of the Mastermind game.

The standard version has 6 different colours for the code pegs. I'm going to assume the colours might be different depending on the individual set one happens to have, so I'll list it out this way. Once you assign a colour to a technique, it should stay that way for all your locks. The basic lock techniques discussed on the other blogs above would require using 4 (and only 4) colours.

• colour a - bump
• colour b - probe
• colour c - rake
• colour d - twist
• colour e - undulate
• colour f - flick

It also has two different colours for feedback pegs, often black and white. These are the pegs the DM will use to simulate what the thief finds out about the lock as he's making his attempt.

• black key peg - you used the right technique at the right time
• white key peg - you used a technique appropriate for this lock, but you used it at the wrong time
• left open (blank) - you used the wrong technique!

So, in this method the coloured clue pegs stand for different picking techniques. What do the slots stand for? Well, not tumblers. Generally, if I understand Wikipedia correctly, most locks are just one tumbler, or at least one tumbler per keyhole. A tumbler has multiple pins, but usually more than four. Thus, the four slots simply stand for how many techniques it takes to open it, or basically how complex the lock is on a scale of 1 to 4. The number of guesses allowed (lines on the board) shows how forgiving the lock is. Something made by gnomes to be highly pick-resistant might only allow 3 or 4 guesses. Some locks may require special techniques that most locks don't, thus using more colours of clue pegs.

How about Telecanter's example where an experienced thief just knows you should never bump a dwarven lock? Easy. If it's a dwarven lock, the DM doesn't put any bump-coloured pegs behind the codemaker screen on the board. Then it's up to the DM and player as to whether the player realises it's a dwarven lock, and knows what to avoid.

Now for the Suspense!!
Each line on the Mastermind board, each guess, takes one round of game time. This is where it really becomes exciting, because everyone knows that the thief picking the lock on the door to the escape route only has 4 minutes before that bugbear guard comes back this way on his patrol! Can he do it?!! They all want him to hurry, but they have to stay quiet!! Every time it's not right, that bugbear gets one minute closer!!! Or that insane cultist has nearly finished summoning Tsathoggua, and every round spent trying to put the right coloured pegs in the right holes to pick the lock on the Necronomicon brings the yawning black gulfs of terror one round closer!!!!
Are you excited yet?!!!?!

If you want to give an experienced thief more clues to reflect their knowledge, use their pick-locks chance (or disarm, as appropriate) to get hints. When you see a black key peg, for example, the picker usually only knows they used a correct technique at the right time (put the right colour peg in the correct hole.) They don't know which step (hole) they got right, they just know they made progress. If they roll under their chance, maybe they do know which step they got right, thereby drastically reducing how long it will take them to finish the lock. Many other types of hints are possible too, perhaps even allowing the thief to know which technique to start with (which colour to put in the first hole) just by recognising the type of lock.