An acceleration sensor for detecting an acceleration in a plane, and having a housing, and a disk magnet arranged in a magnetic fludi stored in the housing. The movement of disk magnet is limited, i.e., a translational movement or rotational movement thereof can occur only in the plane, by projections formed in the housing, between which projections portions of the magnetic fluid having an increased density are formed adjacent to the poles of the disk magnet so that only a translational movement is allowed, or by small circumferential walls between the housing and the disk magnet and radial projections formed between end walls of the housing and disk magnet so that only a rotational movement is allowed. A Hall element issues a signal corresponding to a position of the disk magnet, to thereby determine the acceleration rate.