Abstract: A burglar alarm system mounted in a reinforced doorway and comprising a control circuit having a normally open switch point consisting of a flange projecting from the backer plate towards the striker plate of the door lock, the flange being out of contact with, but close to, a long latch bolt projecting into the latch bolt hole for locking the door, and a contact having an electrical polarity opposite to that of the backer plate. The contact extends towards, but is normally slightly spaced from, the flange whereby the switch point is open and the control circuit is not energized. Displacement of the latch bolt towards the flange by a burglar tool and resultant displacement of the flange towards the contact causes the flange to touch the contact and energizes the control circuit to set off the alarm.

Abstract: A burglar alarm system is mounted in a doorway framing which comprises a reinforcement metal plate extending over a substantial portion of the wall studs and a substantial portion of one minor face of the door jamb, which plate is securely affixed to the wall stud and the minor door jamb face to cover a substantial region of the minor door jamb face adjacent and beyond the door latch bolt hole in the side rail. The alarm system comprises a pair of elongated copper sheets insulated from the metal plate and arranged between the plate and the minor door jamb face. The copper sheets extend side-by-side along a major portion of the reinforcement plate and are insulated from each other. The copper sheets are connected to an electric control circuit energizable to set off a burglar alarm and energized upon electrical contact being made by the sheets through a metal burglar tool used in an attempt to jimmy the door.

Abstract: A door is secured against being kicked in by a doorway construction which comprises a conventional wooden door frame side rail defining a door latch bolt hole in a recessed end portion of one of its major faces and a conventional wall including two-by-four studs adjacent the other major face of the door frame side rail, with the minor faces thereof extending parallel to the wall. The weak point of such a frame is in the region of the hole and this is protected by a reinforcement plate extending over a substantial portion of the wall studs and a substantial portion of the minor face of the door frame side rail overlying the hole. The plate is securely affixed to the wall studs and the door frame side rail and covers this region.