Intrusion sensing device

• US 4,587,517 A
• Filed: 01/28/1985
• Issued: 05/06/1986
• Est. Priority Date: 01/28/1985
• Status: Expired due to Fees

• Current Assignee: AT&T Teleholdings Incorporated (AT&T, Inc.)
• Original Assignee: AT&T Teleholdings Incorporated (AT&T, Inc.)
• Inventors: Till, Robert A. Jr., Engstrom, John G.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US06/695,514
• Time in Patent Office: 463 Days
• Field of Search: 340/542, 340/545, 340/550, 200/61.93, 200/61.08
• US Class Current: 340/542
• CPC Class Codes: E05B 45/086 by transverse movement

Abstract

An apparatus for detecting the forced opening of a door. The apparatus comprises a paper sheet with a frangible conductive path thereon. The sheet has holes therein for the passage of a retractable bolt and fasteners, which are used to secure a strike plate to a frame. The sheet is then concealed behind the strike plate and the conductive loop surrounds the fastener holes. When the door is forced open without retraction of the bolt, a crack appears on the surface of the frame surrounding the fasteners. This crack causes a break in the conductive loop. This break is then detected by a detecting device electrically connected to a part of the loop, thereby triggering an alarm.

Claims

1. An intrusion sensing device for use on a frame having a hole therein for receiving a protrusion, the protrusion extending from a movable member, the intrusion sensing device comprising:

a first portion adapted to be attached to a surface of the frame under a strike plate fastened on the surface of the frame, the first portion including an electrically conductive path which is constructed so that it is broken when the member is displaced in a direction generally parallel to the strike plate surface without retracting the protrusion into the member; and

a second portion joined to the first portion, the second portion adapted to extend between the first portion and a means for detecting the breaking of the conductive path including means for electrically connecting the conductive path of the first portion to the detecting means.

2. The apparatus as recited in claim 1, wherein the protrusion is a retractable bolt.

3. The apparatus as recited in claim 1, wherein the first portion is of a shape to be concealed under the strike plate of the frame.

4. The apparatus as recited in claim 1 wherein the first portion has openings therein to align with the hole in the frame for receiving the protrusion and to surround holes in the frame for receiving fasteners that fasten the strike plate to the frame.

5. The apparatus as recited in claim 1 wherein the combination of the first and second portions comprises a frangible nonconductive sheet having only one frangible conductive path thereon.

6. An intrusion sensing device for detecting movement, without retraction of a latch bolt, of a member from a closed position within a frame to which the member is movably attached, wherein the bolt passes through a latch bolt hole in a strike plate and frame when the bolt is unretracted and the member is in the closed position, and wherein the strike plate is fastened to the frame, the intrusion sensing device comprising:

(a) a frangible, nonconductive, sheet to be bonded to the frame under the the strike plate, the sheet having openings therein that conform to a plurality of latch bolt hole sizes; and

(b) a frangible, conductive path attached to the sheet which path is broken when the latch bolt displaces the strike plate in a direction which is in a plane generally parallel to and generally coincident with the surface of the strike plate.

7. The apparatus as recited in claim 6, wherein the strike plate is fastened to a frame by a plurality of fasteners which extend through the strike plate and into the frame and wherein the conductive path surrounds at least one of the fasteners.

8. An intrusion sensing device for detecting an intrusive opening of a door mounted within a frame without retraction of a latch bolt incorporated in the door and which unretracted bolt passes through a latch bolt hole in the frame and through a latch bolt hole in a strike plate when the door is in the closed position, and which strike plate is fastened to the frame by a plurality of fasteners passing through the strike plate and into the frame, the intrusion device comprising:

(a) a frangible, nonconductive, adhesive sheet adapted to be bonded to the frame and concealed under the strike plate, and having openings therein to surround the latch bolt hole in the frame and to surround fastener holes in the frame; and

(b) a single frangible conductive path on the sheet which path is for surrounding the fasteners and for electrically connecting to a detecting means and which path is broken when there is a crack in the surface of the frame surrounding any of the fasteners, which crack is caused by the displacement of the fasteners in a direction generally transverse to the length of the fasteners when the door is forced open without retraction of the bolt, and which break in the path is detected by the detecting means.

9. The apparatus as recited in claim 8 wherein the sheet is a paper sheet with a removable cover on an adhesive side of the sheet, which side is used to bond the sheet to the frame when the cover is removed.

10. A method of detecting the intrusive opening of a member mounted within a frame without retraction of a latch bolt incorporated in the member and which unretracted bolt passes through a latch bolt hole in the frame when the member is in a closed position, the method comprising the steps of:

bonding an adhesive frangible electrical conductor on the surface of the frame in an area which cracks when the member is displaced in a direction generally perpendicular to the depth dimension of the hole so that the conductor will break in response to the crack; and

electrically connecting the conductor to a detecting means which triggers an alarm when the conductor is broken.

11. A method of detecting the intrusive opening of a member mounted within a frame without retraction of a latch bolt incorporated in the member and which unretracted bolt passes through a latch bolt hole in the frame and through a latch bolt hole in a strike plate when the member is in a closed position and which strike plate is fastened to the frame, the method comprising the steps of:

removing the strike plate from the frame;

bonding an adhesive frangible electrical conductor on the surface of the frame on an area which was covered by the strike plate and which area cracks when the member is displaced without retraction of the bolt in a direction generally perpendicular to the depth dimension of a latch bolt hole so that the conductor will break in response to the cracking in the area;

placing the strike plate back on the frame so that the unretracted bolt can pass through the latch bolt hole in the frame and the latch hole in the strike plate; and

electrically connecting the conductor to a detecting means which triggers an alarm when the conductor is broken.

12. The method as recited in claim 11 wherein the conductor is also placed so that it surrounds a fastener such that the conductor will break when a crack is caused by a minimum force on the fastener in a direction generally parallel to the surface of the strike plate, which force occurs when one opens or attempts to open the member without retraction of the bolt.