RF/ultrasonic separation distance alarm
First Claim
1. An alarm system for preventing loss or theft of at least one article, comprising:
- a transmitter located in a protection device or tag attached to or incorporated in said at least one article; and
a monitoring unit provided with a receiver for receiving the signal from said transmitter and triggering an alarm when the distance between said receiver and transmitter exceeds a predetermined value,said transmitter being an ultrasonic transmitter and said receiver being an ultrasonic receiver, and said monitoring unit further comprising an RF transmitter for periodically transmitting coded RF signals, and each protection device including an RF receiver and a logic unit for activating said ultrasonic transmitter in response to said coded RF signals.
1 Assignment
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Accused Products
Abstract
An alarm system for preventing loss or theft of one or more articles includes an ultrasonic transmitter incorporated in the article(s) to be protected, and a monitoring unit provided with a receiver for receiving the ultrasonic signal from said transmitter and triggering an alarm, for example when the distance between the receiver and transmitter exceeds a predetermined value. The monitoring unit periodically interrogates the protected articles by transmitting a coded RF signal which is decoded and identified by the protecting device of the concerned article, the article emitting an ultrasonic coded signal in response. The ultrasonic coded signal is received by the monitoring unit and triggers an alarm when predetermined conditions are met. Two receiving channels can be arranged in space diverse relationship for better receiving the ultrasonic signal, and the distance between the monitoring unit and the article to be protected can be adjusted.
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Citations
11 Claims
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1. An alarm system for preventing loss or theft of at least one article, comprising:
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a transmitter located in a protection device or tag attached to or incorporated in said at least one article; and a monitoring unit provided with a receiver for receiving the signal from said transmitter and triggering an alarm when the distance between said receiver and transmitter exceeds a predetermined value, said transmitter being an ultrasonic transmitter and said receiver being an ultrasonic receiver, and said monitoring unit further comprising an RF transmitter for periodically transmitting coded RF signals, and each protection device including an RF receiver and a logic unit for activating said ultrasonic transmitter in response to said coded RF signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification