Lock bumping
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Lock bumping is a lock picking technique for opening a pin tumbler lock using a specially-crafted bump key. One bump key will work for all locks of the same type.
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[edit] Bump key
The bump key is made by filing down a key blank (or another key made for the targeted type of lock) to the lowest level in each groove. Slight elevations are left between the groves--if these are too steep, the key will not enter or leave the lock. The tip and shoulder of the key must also be filed down by approximately 1 millimeter. (The shoulder is that part of the key which touches the outer portion of the lock when the key is fully inserted.)
[edit] Bumping
The technique involves inserting the bump key into the lock and tapping the key one or more times with a mallet or similar device, while applying a slight turning force (torque) to the key. After a little bit of practice, this will open the lock. The skill level required to bump a lock is minuscule compared to other lock picking techniques; bumping is a feasible method for compromising locks by just about anyone.
[edit] Explanation
Hitting the key forces it deeper into the lock, allowed by the removed shoulder and tip. The bottom interal pins are forced up because of the elevations between the groves that were left standing. This upward impulse is transmitted to the set of pins that sit immediately on top of the bottom pins. The top pins fly upwards, while the bottom pins remain down. (The same effect is seen when hitting a billiard ball that touches another: only the second ball will move.) As the bottom pins separate from the top pins, the cylinder can be turned and the lock opened.
[edit] History
Lock bumping originated in Denmark in the 1950's[citation needed]. A Dutch TV show explaining the technique was broadcast in April 2005 and found its way to internet video sites in 2006, popularizing the technique considerably.
