| 摘要 |
<p>The security device for electronically checking the direction of movement of moving bodies in a passage (1) comprises at least one pair of unidirectional emitters (7 and 8; 9 and 10) of electromagnetic waves, each one co-operating with a receiver (11, 12; 13, 14) of electromagnetic waves to form an electromagnetic barrier (A, B; C, D). The emitters and receivers are arranged so as to make the electromagnetic barriers substantially transverse to the said passage and separated from one another in a substantially horizontal plane. The receivers are connected in pairs to a direction discriminator (15; 16) connected to an alarm (17; 18), with the result that the movement of a moving body inside the said passage is possible without triggering the alarm only in a specified direction in respect of crossing the said electromagnetic barriers in a specified order. <IMAGE></p> |
