| 摘要 |
An alarm unit (1) for a vehicle comprises four magnet housings (4), each having a vehicle-engaging surface and four magnets (5) received within respective magnet housings (4) and arranged for movement relative to the vehicle-engaging surface of the housing. A spring material (11) biases the magnets (5) into a position in which they are spaced from the vehicle-engaging surface of the housing (4). An electrical sensor (10) detects movement of the magnets (5) relative to the vehicle-engaging surface of the magnet housing.
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