| 摘要 |
An error condition, fault, defect, obstruction, or defective arrangement of viewing angle is determined in a target security device, such as a motion sensor. A plurality of times a fault is detected in a first security device arranged to sense activity in a first zone, the target security device being arranged to sense activity in a second zone overlapping with the first zone; and the error condition may be determined in the target security device when fault in the target security device is not detected for the plurality of times. The second zone may overlap substantially all of the first zone. The first security device may be a door security sensor, a gate security sensor, a keypad or a motion detector. When the first security device is a keypad or user interface, the fault may be an arm or disarm command or an arm/disarm command cycle.
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