| 摘要 |
Range reduction detection apparatus is able to detect blocking of the field of view of an intruder sensor, for instance by a row of boxes. Detection of an event, due to movement or intrusion within the field of view, is arranged to start a timer, which will time-out thereby providing an indication of such blocking unless a subsequent event is detected within the time-period. The subsequent event may be detected by the same sensor or a different sensor. The sensors may be PIRs or microwave Doppler sensors. |
