Security lock for dead-bolt door locks

A locking device for preventing unauthorized retraction of the bolt of a dead-bolt door lock of the type wherein rotation of a key controlled actuator at the outside of the door and of a non-circular manual actuator at the inside of the door selectively effects projection or retraction of the dead bolt, depending in each instance upon the direction or rotation, said locking device comprising:

• A. a base having
• 1. opposite inner and outer faces,
• 2. a round hole therethrough opening to both of said faces, and
• 3. a straight sided guideway that is substantially radial to the axis of said round hole and at one end thereof opens into said hole;
• B. a shroud having an axis, rotatably seated in said round hole with its axis intersecting said inner and outer faces of the base and the axially opposite ends of the shroud accessible at said faces,
• said shroud also having a keeper recess in
• a peripheral side surface thereof;
• C. a socket in the end portion of the shroud that is accessible at the inner face of the base, said socket being of a size and shape to receive and fit said non-circular manual actuator of a dead-bolt lock with which the locking device is associated, so that said non-circular manual actuator may be turned by rotating the shroud, the keeper recess in the peripheral side surface of the shroud being aligned with said guideway when the shroud is in its position of rotation at which the dead-bolt is in its projected position;
• D. means at the end portion of the shroud that is accessible at the outer face of the base by which rotation can be imparted to the shroud;
• E. means for securing the base to the inside of the door with the shroud covering and drivingly connected with said non-circular manual actuator;
• F. a security bolt slidably received in said guideway in the base for movement between a projected operative position engaging said peripheral side surface of the shroud and a retracted inoperative position disengaged from said peripheral side surface of the shroud;
• G. spring means biasing the security bolt towards its projected operative position so that, when free to be moved by said spring means, the security bolt snaps into the keeper recess in said peripheral side surface of the shroud upon rotation of the shroud to its position at which the dead bolt is in its operative position;
• H. a control member for the security bolt selectively movable to a plurality of defined positions;
• and
• I. drive means operatively connecting the control member with the security bolt and through which the operativeness of the security bolt is governed by selective positioning of the control member.