| 摘要 |
A vehicle security system comprises a plurality of sensing units 12, 14, 16 for sensing intrusion or attempted intrusion into the vehicle, and a common control module 10 connected to the sensing units for causing an alarm to be emitted in response to a signal from any sensing unit. To simplify the wiring, each sensing unit is connected to the control module 10 by a single wire. The control module 10 is arranged to vary the voltage on the wire in order to set the operating state of the sensing unit 12, 14, 16 and the sensing unit is arranged to vary the current drawn from the wire to communicate data to the control module. In the embodiment shown, the voltage on each wire is simply switched on to arm each sensing unit, and when a sensing unit detects intrusion it draws a larger current than it would normally. In a second embodiment, Fig. 2, a coded voltage is used to arm respective sensing units and when a sensing unit detects intrusion it modulates the current drawn with a predetermined code recognisable by the control module. <IMAGE> |
