only of the actuating arm 28 the current flow causes rapid resistance heating within the inner portion 32 of the actuating arm and consequential momentary elongation of that portion of the arm the outer arm portion 31 of the actuating arm 28 is mechanically coupled to but electrically isolated from the inner arm portion 32 by posts 36 no current induced heating occurs within the outer arm portion 31 and as a consequence voltage induced current flow through the inner arm portion 32 causes momentary bending of the complete actuating arm 28 in the manner indicated in fig8 and 10 of the drawings this bending of the actuating arm 28 is equivalent to pivotal movement of the arm with respect to the substrate 20 and it results in displacement of the paddle 27 within the chambers 24 and 25 an integrated movement sensor is provided within the device in order to determine the degree or rate of pivotal movement of the actuating arm 28 and in order to permit fault detection in the device the movement sensor comprises a moving contact element 37 that is formed integrally with the inner portion 32 of the actuating arm 28 and which is electrically active when current is passing through the inner portion of the actuating arm the moving contact element 37 is positioned adjacent the second end 38 of the actuating arm and thus with a voltage v applied to the end terminals 34 and 35 the moving contact element will be at a potential of approximately v 2 the movement sensor also comprises a fixed contact element 39 which is formed integrally with the cmos layer 22 and which is positioned to be.