| 摘要 |
<p>A virtual electronic perimeter fence (20) includes at least a first (12), second (14) and third (16) fence post each including an emitter (12E, 14E, 16E) for emitting a beam of infrared light at a predetermined frequency. The first (12), second (14) and third (16) fence posts include a receiver (12R, 14R, 16R) for receiving the predetermined frequency of infrared light emitted from a designated fence post (12, 14, 16). A beam of infrared light of a first frequency is emitted from the first fence post (12) to the second fence post (14) and a beam of infrared light of a second frequency is emitted from the second fence post (14) to the third fence post (16) and infrared light of a third frequency is emitted from the third fence post (16) to the first fence post (12) for providing a virtual electronic perimeter fence (20) that provides an alarm if an interruption occurs in the beam of infrared light while eliminating cross-signals therebetween. A light, sound and video system may be provided.
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