Lock bumping is a way of picking locks that utilizes special keys, called bump keys, that take advantage of the mechanics of pin tumbler locks. When the bump key is inserted into a lock and bumped with a hammer, the force sends lock tumblers into position and allows the lock to be disengaged.
Lock bumping is only effective for opening a pin tumbler lock. The first patent for this technique appeared in 1928, when the bump key was originally called a rapping key. The bump key must be the appropriate size for the lock, and each ridge in the key must be cut to maximum depth.
When bumping a lock, the key is inserted into the key way slightly less than full insertion. Bumping the key inward forces it further into the key way, and the specially designed teeth of the key cause a slight impact that forces all of the bottom pins in the lock. The key pins transfer this force to the driver pins while the key pins stay in place. The driver pins "jump" from the key pins for a fraction of a second providing the user with the opportunity to turn the lock and disengage it.
Installing chain latches and deadbolt locks or the modification of existing locks helps to mitigate the susceptibility of break-ins via lock bumping.