Security system with interference detection

• US 4,737,771 A
• Filed: 07/23/1986
• Issued: 04/12/1988
• Est. Priority Date: 07/23/1986
• Status: Expired due to Fees

• Current Assignee: Notifier Company (Honeywell International Inc.)
• Original Assignee: Emhart Industries, Inc. (Stanley Black & Decker, Inc.)
• Inventors: Coash, Ronald J.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US06/888,495
• Time in Patent Office: 629 Days
• Field of Search: 340/539, 340/501, 340/500, 340/506, 340/531, 340/536, 455/1, 455/67, 455/222, 455/224, 455/154, 455/155, 455/158, 455/63, 342/14, 342/20, 324/57 N, 375/26, 375/99
• US Class Current: 340/539.1
• CPC Class Codes: G08B 25/007 Details of data content structure of message packets; data protocols
• CPC Class Codes: G08B 25/10 using wireless transmission systems G08B25/009 takes precedence
• CPC Class Codes: G08B 29/18 Prevention or correction of operating errors G08B29/02, G08B29/12 take precedence
• CPC Class Codes: H04K 3/222 wherein jamming detection includes detecting the absence or impossibility of intelligible communication on at least one channel
• CPC Class Codes: H04K 3/88 related to allowing or preventing alarm transmission

Abstract

A security system having one or more sending units for transmitting an electromagnetic signal representative of a condition such as fire, smoke, intrusion, battery condition, an emergency or other condition to a central receiving unit. Upon reception of an electromagnetic signal, the receiving unit provides an electromagnetic carrier detect signal to a microprocessor. A software timer within the microprocessor keeps track of the time over which the carrier is detected. If the carrier detection continues for a time longer than about 20 seconds, then a jamming indication signal is provided to one or more outputs. While the system is being jammed, alarms are ignored thus avoiding false alarms due to interference.

Claims

1. A security system comprising:

sensor means for sensing a condition and producing a data signal representative of the condition;

transmitter means for transmitting an electromagnetic signal modulated by said data signal;

receiver means for receiving said electromagnetic signal and providing a received data signal;

interference detection means for detecting interference with said electromagnetic signal and producing a control signal; and

output means responsive to said received data signal and said control signal for providing an indication of said condition.

2. A security system as in claim 1 wherein said output means includes a means for providing an indication that interference with said electromagnetic signal is present.

3. A security system as in claim 1 wherein said interference detection means comprises a means for determining that a signal has been received by said receiver continuously for a predetermined time.

4. A security system as in claim 1 wherein said interference detection means includes a means for producing a carrier detect signal indicative that an electromagnetic wave is being received by said receiver, timing means for producing a timing signal, and a means responsive to said carrier detect signal and said timing signal for producing said control signal.

5. A security system as in claim 2 wherein said output means includes a means for indicating that said interference has occurred at a prior time.

6. A security system as in claim 5 wherein said means for indicating that said interference has occurred comprises a means for recording the time when said interference occurred.