| 摘要 |
A security system for monitoring the presence of one or more objects in a monitored zone. The system comprising an antenna and at least one tag having a tuned resonant circuit, the tag being associated with one or more objects to be monitored. A transmitter coupled t o the antenna operable to transmit at one of a plurality of frequencies in response to a frequency selection signal; a receiver coupled to said antenna and for producing a tag detection signal for stopping said cycling of said transmitter frequencies in response to a signal receive d at said receiver from said tag thereby causing said transmitter to transmit at a single frequency when a tag is detected. Means for decreasing the output power of the transmitter when the received signal is above a predetermined level.
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