| 摘要 |
Apparatus for monitoring opening of sealed enclosures, especially, but not exclusively, sealed containers containing goods-in-transit, such as goods vehicl es, maritime containers or transport containers of the kind carried by tractor-trail ers, ships, trains or aeroplanes comprises a radio receiver unit having at least one antenna for reception of radio signals. The receiver unit is housed within the enclosure and operates to scan a predetermined band of radio frequencies, periodically or continuously, and detect a sudden change in signal level. When it detects such a change in radio s ignal level, the receiver generates an alarm signal. Alternatively, the receiver may d etect the difference between internal and external radio signal levels and determine the c ontainer to have been opened if the difference is less than a preset threshold.
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