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Wireless Alarms - How They Work and Don't Work (From Physical Security - Readings From Security Management Magazine, P 163-173, 1986, Shari Mendelson Gallery, ed. - See NCJ-101017)

NCJ Number
J Gant
Date Published
11 pages
This paper discusses the operational principles of new wireless alarm systems used in the United Kingdom and notes alarm systems used in the United Kingdom and notes the advantages and disadvantages of each system.
Infrared systems transmit a stream of infrared light pulses in a coded form which are received by a diode in the equipment. Interruption of the stream triggers an alarm. This system is relatively free of external electronic interference and has the capacity to penetrate walls. A disadvantage is that operational requirements require the units to be visible. Line carrier systems use transmitter units, typically of cigarette package size, in existing electrical sockets. Disadvantages of this system are vulnerability to external monitoring and modification as well as the requirement that signals be used on wiring with the same phase. Ease of installation is the primary advantage. Advantages of ultrasonic systems are their protection against external interference and their ability to overcome wave cancellation problems associated with placement. The primary disadvantage is the inability to signal through barriers. The principal advantages of radio systems are low cost and ease of installation. The primary disadvantage is false alarms from external interference, increasing the likelihood that police will not respond to such alarms.