3810147 is referenced by 109 patents and cites 6 patents.

An electronic security system especially adapted for use in retail stores and employing a multi-frequency resonant tag circuit having distinct frequencies for detection and deactivation. A transmitting system provides an electromagnetic field within a controlled area at a frequency which is swept through a range including the detection frequency of the resonant circuit. In the presence of a tag circuit within the controlled area and operative at the detection frequency, pulses are detected by a receiver which includes noise rejection circuitry for discriminating true signals from noise. The receipt of a predetermined number of signal pulses within a prescribed interval of time causes an alarm actuation. The resonant circuit is formed by printed circuit techniques as a relatively small tag which can be affixed to an article of merchandise. The tag includes a fusible link integrally formed as part of the circuit and which can be fused upon application of an electromagnetic field of predetermined magnitude at the deactivation frequency of the resonant circuit. Deactivation of the tag destroys the resonant properties of the tag at the detection frequency such that a deactivated tag produces no alarm when passing through a controlled area.

Title
Electronic security system
Application Number
05/214,361
Publication Number
3810147
Application Date
December 30, 1971
Publication Date
May 7, 1974
Inventor
Lichtblau George Jay
Agent
Weingarten Maxham & Schurgin
IPC
G01s 09/56
G08B 13/24
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