Abstract: A Z-bar security system, one which is provided with a key and a secured latch, is combined with an electronic alarm and monitoring system. This combination provides the maximum degree of both mechanical and electronic security. In a preferred embodiment, a Z-bar latch assembly has a three-position rotatable cylinder which is operable by a key from outside of the door. These three positions correspond, respectively, to "open", "viewing" and "closed" positions of the door.

Abstract: A system for locking a door can: (1) lock the door in dead bolt fashion in three modes, (2) allow the door to open a limited distance, or (3) allow the door to open freely. The system has a door-mounted latch assembly that includes a base plate, an intermediate link pivoted to the base plate, and a mode selection and latching assembly that is pivoted to the intermediate link. A latch plate is mounted on the door frame in juxtaposition to the door-mounted latch assembly. The latch plate has a tubular portion with an opening for receiving the latch member. A sleeve fits inside the tubular portion of the latch plate. When the latch member is engaged in the tubular portion of the latch plate, the sleeve can be rotated so that the latch member is engaged to the sleeve in a secured position. The latch plate includes a locking mechanism to releasably lock the sleeve into the secured position. The locking mechanism may be a spring-loaded pin mounted within the sleeve.

Abstract: A system for locking a door can: (1) lock the door in dead bolt fashion, (2) allow the door to open a limited distance, or (3) allow the door to open freely. The system has a door-mounted latch assembly that includes a base plate, an intermediate link pivoted to the base plate, and a mode selection and latching assembly that is pivoted to the intermediate link. The latch assembly also includes a high strength, "T"-shaped latch member, and camming means to slide the latch member back and forth as a control knob is rotated. A latch plate is mounted on the door frame in juxtaposition to the door-mounted latch assembly. The latch plate has a cylindrical portion with a vertical slot for receiving the "T"-shaped latch member. A cylindrical sleeve fits inside the cylindrical portion of the latch plate. Like the cylindrical portion of the latch plate, the sleeve has a vertical slot for receiving the latch member. The sleeve also has a horizontal slot running perpendicular to and intersecting with the vertical slot.