Side view illustration of a) reset and b) trigger force tests. The angles are all in reference to the extended position of the metal strip. Theoretically, the angle (θ) can range from 0° to 180°. However, restricted by the device design, the angle is below 90°. (Blue: bistable metal strip; black: pivot fixed onto the middle of the metal strip; silver: pulling thread; box with “F”: force sensor)