Chain-type door latch and alarm

• US 4,233,595 A
• Filed: 11/30/1978
• Issued: 11/11/1980
• Est. Priority Date: 11/30/1978
• Status: Expired due to Term

• Current Assignee: People Protection Products Incorporated
• Original Assignee: Christoph Emmerich KG
• Inventors: Landkammer, Franz J.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/964,923
• Time in Patent Office: 712 Days
• Field of Search: 340/545, 340/548, 340/542, 200/61.93
• US Class Current: 340/542
• CPC Class Codes: E05B 45/06 Electric alarm locks E05B45/005 takes precedence
• CPC Class Codes: E05C 17/365 Security chains
• CPC Class Codes: G08B 13/06 by tampering with fastening

Abstract

A door latch and alarm apparatus has a support mounted on the door and a support mounted on the doorjamb. A relatively inextensible and flexible element is anchored to the door support and has a free end provided with an end piece fittable in a latch on the doorjamb support. A pair of conductors, one of which may be the inextensible and flexible element, extend from the door support to the end piece where they are connected together via a resistor. At their other ends these conductors are connected to a resistance detector which operates an alarm whenever the resistance between the two conductors increases, as when the conductors are broken, and whenever it decreases, as when they are short-circuited.

Claims

1. A door latch and alarm apparatus comprising:

a door-mounted support;

a doorjamb-mounted support;

a relatively inextensible and flexible element anchored to said door support and having a free end provided with an end piece receivable in said doorjamb support;

latch means including key-operable mechanism on said doorjamb support for releasably securing said end piece thereto, whereby the door can open a limited distance from the doorjamb before said element becomes taut and impedes further opening;

circuit means including a pair of conductors extending between said door support and said end piece and a relatively fragile connector in said end piece forming a closed conductive path with said conductors, said connector being so much weaker than said element that when same is stressed beyond a certain limit said connector interrupts said path before said element breaks; and

alarm means on said door-support connectable to said conductors for emitting an alarm when said path is interrupted.

2. The apparatus defined in claim 1 wherein said circuit means includes a resistor connected between said conductors at said end piece, said alarm means including means for detecting the resistance between said conductors and for emitting said alarm when said resistance increases or decreases substantially.

3. The aparatus defined in claim 1 wherein said circuit means includes a cable separate from said element and having said pair of conductors.

4. The apparatus defined in claim 3 wherein said element is a chain.

5. The apparatus defined in claim 3 wherein said element is shorter between said door support and said end piece than said cable.

6. The apparatus defined in claim 1, a cable extending between said door support and said end piece and having a plurality of wires constituting said element and said conductors.

7. The apparatus defined in claim 6 wherein said cable has two such wires, one constituting said element and one of said conductors and the other constituting the other conductor.

8. The apparatus defined in claim 6 wherein said cable has three such wires, one constituting said element and the other two constituting said conductors.

9. The apparatus defined in claim 1 wherein said conductors are relatively strong between said end piece and said door support and relatively fragile in said end piece.

10. The apparatus defined in claim 9 wherein each of said conductors is formed in said end piece as a fragile conductive strip constituting said connector.

11. The apparatus defined in claim 10 wherein said doorjamb support includes at least one screw securing said doorjamb support to said doorjamb and having a shank extending between and past said strips and a head overlying and overlapping said strips, whereby said strips can be pulled into short-circuiting electrical contact with said head.

12. The apparatus defined in claim 10 wherein said strips each have one end connected to the respective conductor and another end connected to the other strip.

13. The apparatus defined in claim 1 wherein one of said supports is provided with a relatively fragile anchor for said conductors and the other of said supports is provided with a more substantial anchor for said conductors.