When the two peices of hardware are together the lock is then secure denying unauthorized access. This vertical interlocking feature prevents the door from being pried open by a pry bar. The Jimmy Proof lock can be installed as a single cylinder or double cylinder setup. The single cylinder setup will require a keyed entry only on the exterior, while on the interior there is a knob or lever which can lock and unlock the locking mechanism. The double cylinder setup would require keyed entry both on the exterior as well as the interior, which applies to locking and unlocking the lock mechanism.