| 摘要 |
<p>An alarm system comprises a plurality of alarm units (11), each of which includes means for transmitting an alarm signal containing data indicative of the orientation of the alarm unit; a plurality of roadside receiving units, each of which includes means (10) for receiving alarm signals transmitted from an alarm unit within a certain range, and means (16) for retransmitting a signal to a control centre (6), which includes means from receiving signals transmitted from the receiving units; and means (3, 5) connecting the receiving units to the control centre. <IMAGE></p> |
