Knob locks are frequently installed in residential situations on exterior doors in addition to deadbolts, and are sometimes used as the primary source of security for doors. Knob locks are basically made up of a knob with a lock cylinder and key system. Knob locks are a fairly common when it comes to home (interior door locks). However, they should be strictly used for internal doors. The reason behind this is that, the lock cylinder is located within the knob and by simply breaking off the knob, the lock mechanism is destroyed. As such, they should not be used for external doors. The problem lies in the fact that the lock cylinder is in the knob itself and not the door. In almost all setups, they can be broken off the door with a hammer or bypassed using pliers or a wrench behind the knob, completely bypassing the locking cylinder. If you currently have knob locks, consider replacing them with simple passage knobs as it will provide almost as much security as long as you are using deadbolts on the same doors.