In vehicle control systems such as ABS (anti-lock braking system) or active suspension control, sensors for detecting longitudinal and/or lateral acceleration of vehicles (acceleration of up to ± 9.8 m/s2, with frequency range of DC to 20 Hz) is necessary.The principle of acceleration detection for this sensor is as follows. A permanent magnet levitates steadily in magnetic fluid by the action of the magnetic field generated by the magnet itself. The magnet moves by the application of acceleration on the mass of the magnet. This change of position of the magnet is detected by the Hall element, and thus acceleration is measured as an electrical signal.This sensor consists of only magnetic fluid, a permanent magnet, housing, a pair of Hall elements and an electronic circuit. With this simple construction, however, this sensor has high shock resistance and detects acceleration accurately at low frequency ranges, by utilizing magnetic spring force and the damping effect of magnetic fluid. Thus, this sensor is effective for the detection of vehicle acceleration.