| 摘要 |
The device comprises, in combination, a radio transmitter, a radio receiver 2, an audible 3 and/or visual 23 alarm device and means 4 for adjusting the triggering threshold of the alarm when the signal is transmitted by the transmitter and received by the receiver with a strength below a certain threshold. It preferably further comprises a switch 11 and a changeover switch 19 allowing adjustment, by the means 4, without causing the audible alarm 3 to sound; the members 11, 4 and 19 may advantageously be controlled by means of a single control knob. <IMAGE>
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