Dual signal electromagnetic article theft detector
First Claim
1. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:
- a. a transmitter for transmitting first and second signals in the vicinity of said exit, said first signal being transmitted as a series of periodic pulses having a first predetermined period of time therebetween;
b. receiver means carried by said article, said receiver means including;
i. an electrical power source;
ii. a first receiver for detecting the presence of said first signal, said first receiver being continuously coupled to said electrical power source for continuously receiving electrical power therefrom, said first receiver generating an enabling signal upon detecting said first signal;
iii. a second receiver for detecting the presence of said second signal and providing an alarm in response thereto, said second receiver generating a disabling signal upon failing to detect said second signal within a second predetermined period of time after said enabling signal is generated, said second predetermined period of time being shorter than said first predetermined period of time; and
iv. power switching means responsive to said enabling and disabling signals for selectively electrically coupling said electrical power source to said second receiver following the generation of said enabling signal and decoupling said electrical power source from said second receiver means following the generation of said disabling signal for lessening the amount of electrical power drained from said electrical power source during instances when said receiver means is exposed to said first signal in the absence of said second signal.
4 Assignments
0 Petitions
Accused Products
Abstract
A transmitter emits a pulsed radio signal and a digitally encoded radio signal near each exit of a protected premises. Monitored articles carry a receiver having a first circuit for receiving the pulsed signal, a power source, and a power switch for coupling the power source to a second circuit on detection of the pulsed signal. The second circuit receives the digitally encoded signal as multiple, serially-transmitted code bits. It also contains a clock for generating timing signals synchronized by the pulsed signal in order to distinguish a plurality of code bit intervals. A processor, an associated memory, and an address counter compare the digitally encoded signal with a stored bit pattern. On receiving an improper code bit, the processor causes the power switch to decouple the power source from the second circuit to conserve power. If the received signal matches the stored bit pattern, power is maintained to the second circuit. Alarm circuitry is triggered by overflow from the address counter. The address counter is reset each time the pulsed signal is received and thus produces no overflow, but when the article is removed from the protected premises, the address counter is allowed to overflow triggering the alarm circuit.
37 Citations
20 Claims
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1. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:
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a. a transmitter for transmitting first and second signals in the vicinity of said exit, said first signal being transmitted as a series of periodic pulses having a first predetermined period of time therebetween; b. receiver means carried by said article, said receiver means including; i. an electrical power source; ii. a first receiver for detecting the presence of said first signal, said first receiver being continuously coupled to said electrical power source for continuously receiving electrical power therefrom, said first receiver generating an enabling signal upon detecting said first signal; iii. a second receiver for detecting the presence of said second signal and providing an alarm in response thereto, said second receiver generating a disabling signal upon failing to detect said second signal within a second predetermined period of time after said enabling signal is generated, said second predetermined period of time being shorter than said first predetermined period of time; and iv. power switching means responsive to said enabling and disabling signals for selectively electrically coupling said electrical power source to said second receiver following the generation of said enabling signal and decoupling said electrical power source from said second receiver means following the generation of said disabling signal for lessening the amount of electrical power drained from said electrical power source during instances when said receiver means is exposed to said first signal in the absence of said second signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification