| 摘要 |
A detector for detecting the presence of an object at a prescribed location, the detector comprising:- an optical source arranged for emitting a collimated optical beam towards the prescribed location, an optical detector for detecting optical signals emitted by said optical source, an optical collector arranged for collecting optical beams scattered by an object located at the prescribed location and for forwarding said optical beams to said optical detector for optical detection; and control circuitry for monitoring output of said optical detector and for determining the presence or absence of an object at said prescribed location by monitoring said output.
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