Abstract: A key operated dead bolt lock includes one or a pair of standard threaded mortise cylinders. The lock further includes set screws, inaccessible from either side of a door in which the lock is installed, which prevent rotation of the cylinders. The cylinders hold cylinder collars in place to prevent access to the bolt from the side.

Abstract: A conventional rotatable tumbler combination lock of the type having notched rotatably mounted tumblers, a notched rotatably mounted drive plate, a bolt plate and bolt movable between locked and unlocked positions, a lever pivotally mounted to said bolt plate and having a fence for engagement with said tumbler notches and a dog for engagement with said drive plate to allow movement of bolt to said unlocked position, the improvement comprising including a scrambler mechanism which includes a rod having one end rotatably mounted to the bolt plate and another end adapted for engagement of detents on the tumblers. The rod engages said detents when the lock is in the open position and when the lock is closed, the rod spins the tumblers and the engagement of the dog with the drive plate notch and the fence with the tumbler notches is upset.