| 摘要 |
A motion detector, for example a passive infrared detector, is used for detecting a person (3) in an area under surveillance as soon as this person is moving. If an output signal (7) is present at the output (6) of the detecting circuit (1), a timing circuit (8) is triggered which increases the sensitivity of the detecting circuit (1) for a predetermined period of time (t) so that even a person (1) who is moving very little, for example, is sitting, can be detected. As long as a person (1) is detected in the room, an electrical system, for example an illuminating device (21), remains switched on but it is switched off automatically when there are no persons present. <IMAGE>
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