Most locks (including deadbolts) use a cylinder with pin tumblers, and a key. The cylinder is a common locksmithing device that allows a locksmith to easily remove and replace the locking mechanism. The pin tumblers represent a series of spring-loaded pins. When the pins are all pushed back to the proper position, the lock is freed and can be turned. A key's undulating teeth are made to match the settings of these pins. The wrong key will either fail to press the pins into the proper position or simply won't fit into the keyhole. Lockpicking works by using picks to push each pin into place.
Lock and Key
Why is a Deadbolt Different from a Regular Lock?
The common door knob lock is of a spring-loaded design. This means the bolt itself is held in place by a spring, which is less secure because the bolt can be moved simply by applying force and compressing the spring ("jimmying the lock"). Deadbolts, on the other hand, can only be moved by the proper rotation of the cylinder. This makes them more resistant to tampering.
There are single and double cylinder deadbolts, which refers to how many keyholes there are (two meaning one for the inside and outside). Single cylinder deadbolts may or may not be accompanied by a thumbturn lever on the inside. The assembly of a deadbolt will often reflect considerations for the door in question. For example, a double cylinder deadbolt is common for doors with glass panes that would offer easy access to a thumbturn lever or door knob, while a single cylinder without thumbturn lever would be normal for exit-only doors.