A bump key is a key with pin positions that are cut to the deepest possible depth so that the key can be used to pick a pin-tumbler lock. To be effective, the key may also have to be further altered by sanding or filing the key tip and shoulder.
To use a bump key, insert it into the lock and then firmly tap or bump it to trigger the lock. The lock and the blank key used to make a bump key must be made by the same manufacturer. Bump keys are used by locksmiths, but they can be used by criminals to gain entry to homes or businesses.