Pin tumbler locks are comprised of a series of spring loaded pin stacks. Each pin stack consists of two pins that are stacked one atop the other, the key pin (which touches the key) and the spring loaded driver pin. When the correct key is used, the pins line up along the "shear line" of the cylinder, allowing it to turn. The key pins are of different lengths and require an appropriately cut key to allow them to align properly along the shear line so the cylinder is free to turn. If the wrong key is used, the pins will be misaligned and will prevent the cylinder from turning.

With bump key lock picking, a specially crafted bump key is inserted to one notch shy of full insertion. It is then tapped, or bumped, completely in. The teeth all contact the key pins simultaneously, transmitting an impact force to the driver pins. This force causes the driver pins to jump for a moment, enough that they will clear the cylinder and travel into the lock housing. If a slight rotational force is applied concurrently with the lock bumping, the cylinder will turn in the brief moment that the pins are separated.

There are very few pin tumbler locks that are resistant to bump key lock picking. High quality and hardened steel locks are more vulnerable to bumping than are standard locks. Lock bumping is a simple but highly valuable skill for a locksmith to possess.