Thief skills, redux

I think I've finally got my thoughts all settled and sorted on how the skills of the thief class will work in my game.  This all started out as an effort to make low-level thieves not totally incompetent at their profession while still allowing them to benefit from gaining levels.  My aim was to utilize the existing percentage tables, but interpreted in a way that emphasizes time and risk management rather than a simple pass or fail roll that low-level thieves would fail far more often than not.  These interpretations should work with the thief skill tables of any old school D&D edition or clone.

Included are optional ability score modifications to the skill roll, which apply a +5% bonus (or -5% penalty) for each point of the standard ability modifier for the given score, i.e. -15% for an ability modifier of -3 to +15% for a modifier of +3.  Also included are suggestions for non-thief characters to attempt some of the functions and activities normally considered to be the province of thieves alone.  (Optional modifiers should apply only for actual thief characters, not to non-thieves attempting thiefly skills.)

Open Locks:  A thief is not limited to one attempt per lock.  The first attempt is to pick the lock in one round.  Failing that, the thief may make a second attempt at picking it in one minute.  If that fails too, then each additional attempt takes one full turn.  Any roll of 00 jams the lock in some way - something inside the lock breaks, or a pick snaps off, and no further attempts may be made. The higher a thief's level, the more likely that he or she can spring a lock quickly and cleanly, but any thief can open just about any lock, given enough time.

Optional modification: Dexterity

For non-thieves:  A character of any other class may make a one-time attempt with a 5% chance of success to pick a lock in 1d4 turns.  The lock is jammed on a roll of 75 or higher.  Any character may attempt to break open a lock by force.  This is noisy, destroys the lock, and may, depending on circumstances, damage the contents of a locked container.

Find Traps: Area traps are resolved through player-referee dialog and don't require the specialized skills of the thief.  Traps on doors and containers are resolved using the thief's percentages.  Find Traps may be attempted as many times as desired, at a cost of one turn per attempt, rolled secretly by the referee.  A container or door may be trapped multiple times, each requiring a successful roll to find.

Optional modification: Intelligence

 For non-thieves:  As mentioned above, area traps can be detected by anyone.  Even chest and door traps may have clues that a non-thief can detect and interpret - a skeleton sprawled in front of the chest, a dart stuck in the wall opposite the door, etc.  Otherwise, any character specifically looking for traps has a 5% chance to notice them.  The attempt may be repeated if desired.

Remove Traps: A thief may make more than one attempt at removing a trap, but at increased risk.  The first attempt triggers the trap only on a roll of 00.  If the thief tries again, it represents pressing his/her luck and fingers-crossed guesswork (e.g. "Do I cut the red wire or the blue one?") The trap is triggered on a roll greater than twice the chance of success, or a roll of 95 or greater.  Third and subsequent attempts set off the trap on any failed roll.  Each attempt is considered to take one turn.

Optional modification: Dexterity

For non-thieves: Removing traps by an untrained person is a dangerous and foolhardy endeavor; the chance of success is the same as a first level thief, but failing by 10 or more triggers the trap, even on the first roll.  Second and subsequent attempts trigger the trap on any failed roll.

Pick Pockets: This skill works without modification from Moldvay/Cook Basic; i.e. the chance is modified by -5% for each level of the target above 5th, and on a roll greater than twice the adjusted chance of success the attempt is noticed by the victim. 

Optional modification: Dexterity

For non-thieves:  A base 10% chance of success, modified by the target's level as normal, with the usual chance of detection.  Clearly risky business for the unskilled!

Climb Walls: A thief may remain on a wall (whether actively climbing or simply holding on) for one round per level before a check need be made; in other words, no roll is needed to attempt a climb, only to continue it or maintain position over time.  Climbing is at the rate of 5' to 20' per round, depending on the difficulty of the wall, at the referee's discretion; the player should be informed of this prior to beginning the climb.  A failed climbing roll results in a fall from the character's elevation at the time of the failed check.  For each successive period of climbing or clinging to the wall, the check is made at a cumulative -10% penalty.  For example, a 3rd level thief would make an unmodified check after 3 rounds, a roll at -10% at 6 rounds, -20% at 9 rounds, and so on.

Optional modification: Strength

For non-thieves: A non-thief character not wearing metal armor must roll under his or her Dexterity score on 1d20, to begin the climb.  Thereafter, the character may remain on the wall for a number of rounds equal to half his or her level, rounded up, before another check must be made.  Each subsequent check is made with a cumulative +2 penalty.  A character with 18 Dexterity is thus slightly inferior to a 1st level thief.  Climbing of this sort cannot be attempted while heavily encumbered.

Move Silently: On a successful roll, the thief is moving with absolute silence, making no noise discernible to human or demi-human ears, and will automatically surprise anyone not looking in his or her direction.  On a failed roll, the thief is still moving quietly, gaining +1 to surprise opponents.  All attempts at silent movement are at half normal movement rate; a thief who desires only quiet movement may do so automatically at full movement. 

Optional modification: Dexterity

For non-thieves: Non-thieves may not move silently, but move quietly on a roll of 1-4 on 1d6, modified by the character's Dexterity bonus or penalty, with an additional penalty of +1 for wearing metal armor (but never greater than a 5 in 6 chance nor less than 1 in 6.)  Quiet movement is at half normal movement rate.  Moving quietly improves the odds of surprising opponents and reduces the chances of being surprised by 1 in 6, and may also reduce wandering monster checks at the referee's discretion.

Hide in Shadows: On a successful roll, the thief manages to conceal him- or herself in a patch of darkness.  This can be attempted only when shadows are present, and is automatically unsuccessful with regard to anyone actually looking at the thief when the attempt is made.  The thief must remain motionless in order to remain hidden.  The thief may break from cover and attempt a backstab attack on any creature unaware of his or her presence and passing within 10' with automatic surprise.  Note that this skill may be used in combat, provided the thief is not engaged in melee, and that all enemies are at least potentially distracted in the chaos of battle and unable to keep an eye on the thief.

Optional modification: Wisdom

For non-thieves: Hiding in shadows is simply not possible for non-thieves.  Hiding in the ordinary sense is accomplished by dialog between player and referee.  A character who successfully hides may ambush others, gaining a +2 bonus to surprise.

Hear Noise: This skill applies to listening for and discerning sounds which would otherwise go either completely unheard or fail to register in the awareness of an untrained person.  No roll is needed for something that, in the referee's judgment, would be audible to anyone, such as a conversation at normal speaking volume behind an ordinary door.  At the referee's option, a check may enable the thief to discern the actual content of such a conversation, though, provided the thief understands the language being spoken.

Optional modification: Wisdom

For non-thieves: The rules provide for a 1 in 6 chance for non-thief humans, and 2 in 6 for demi-humans, to detect noise as a thief character does.

Read Languages: Rather than gaining a flat 80% at 4th level, this skill follows the same progression as Open Locks.

Optional modification: Intelligence

For non-thieves: Not applicable.  Learn the language or use magic.

Previous posts on related topics:
Picking the lock
Thief dilemma: traps
Stealth and surprise