Abstract: An acceleration sensor comprises a housing formed with a hollow cavity deing a sensing direction. An acceleration sensing conductive mass is releasably mounted in the cavity. The mass is released by a cutting member which severs the releasable mounting of the acceleration sensing mass. A force applying assembly is activated to cause movement of the cutting member. Switch electrodes are arranged at the lower end of the housing cavity. The mass falls through a predetermined distance and bridges the switch electrodes. The sensing mass, when severed, may move in incremental steps due to the use of a two-stage releasing assembly. Sensing transducers may be located along the falling path of the acceleration sensing conductive mass.