Abstract: A security chain lock for doors features a chain housing and guideway attached to the interior side of the door and coupled securely to door lock cylinder housing means. An extension of the chain housing laps the edge of the door through which the door lock bolt projects and is firmly anchored to such edge. A keeper mounting bracket is rigidly secured to the inner face and to the edge of the door frame which faces the door edge. A keeper housing is pivotally secured to said mounting bracket and receives a spring-urged keeper projecting from a reciprocatory release element joined to the keeper housing and adapted to enter an inaccessible chamber of the door frame when the keeper housing is pivoted in response to partial door opening from the inside while the chain lock is active. A coacting latch element connected with the extensible and retractable chain means is shiftable by an interior knob into active coupling engagement with the keeper in the keeper housing.

Abstract: A chain lock for doors is greatly reinforced by the placement of a first chain end anchor behind an angle retainer which embraces a square corner of the adjacent door frame and is further secured by a serrated clamping plate in a plane perpendicular to the first chain end anchor. The opposite chain end anchor is received in a slot of a retainer plate which similarly embraces a corner of the swinging door and is further held securely by an extension which is locked to an adjacent interior portion of a door lock cylinder housing assembly.

Abstract: A lock cylinder housing assembly is received in a through bore of a door and coupled therein without the use of external or internal machine screws. A coacting dead bolt assembly in a bore formed in the door at right angles to the through bore bridges the through bore and extends through a transverse passage of the housing assembly to prevent rotation of the assembly or disassembling thereof from the exterior or interior of the door. A catch release mechanism on the dead bolt assembly is accessible only when the door is open to allow releasing of the catch means which allows removal and disassembly of the housing assembly at the inner side of the door.