In the most common type of lock (the pin tumbler lock), as you push the key in, the teeth of the lock slide underneath the pins, inevitably resulting in wear of both the key's teeth and the lock's pins.

This idea prevents that, and also prevents lock bumping, and should also make the lock much more pick resistant.

Above the entrance to the keyhole, there's a wheel. There are several cylindrical holes bored through this wheel, with a pin in each cylinder; these are arranged radially. All of the pins in the lock are the same length as each other, and each pin is a single piece. In between uses, each pin is in the outward-most position in it's cylinder. Friction keeps each pin in it's proper position.

As the key is pushed into the keyhole, the wheel turns, pushing each pin against the key tooth that is passing underneath. The pins remain in their new positions after the teeth have passed, again due to friction.

When the key is entirely in the lock, the user tries to turn it; this pushes the wheel sideways (without turning the wheel), through an opening that will only pass the wheel if every pin is pushed in the correct amount. Pins that aren't in enough will of course meet the outside edge of the hole; for pins that were pushed too far inward, their tops meet an obstruction which passes through the inside of the wheel.

If the wheel can pass through the opening, it pushes on a lever which engages or disengages the locking bolt.

Locks are keyed differently from one another by varying the shape of the opening through which the wheel must move.

A mechanism is required to make sure the wheel is turned at the same rate as the key is pushed in, and another mechanism is required to make sure that the pins are reset between uses.

Both of these needs can be accomplished by having the tip of the key push against a lever, which simultaneously turns the pin wheel, and compresses a spring.

As the key is removed from the lock, the spring pushes on the lever, and turns the pin wheel backwards. For each pin, just after it moves past the key tooth that had pushed it inwards, either it gets pushed outwards due to the "top" (inner surface) sliding across a ramp, or pulled outwards by an appropriately located permanent magnet.

The impossibility of bumping should be obvious.

Pick resistance is provided by the fact that the lock effectively measures the height of every key tooth first, and then, separately, tests all of these measurements simultaneously. This should eliminate most of the tactile or auditory feedback that a lock pick might expect to use to determine which pins he has guessed the correct heights of.

Pick resistance can be truly maximized if the lock can only be turned if the key is fully inserted, and if the pins are only reset when the key is fully removed -- this would require a slightly more complicated mechanism, but it shouldn't be particularly difficult.
-- goldbb, Jul 15 2011

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