accelerometer/motion sensor! These spring-vibration switches are high sensitivity non-directional vibration induced trigger switches. Inside is a very soft spring coiled around a long metal pin. When the switch is moved, the spring touches the center pole to make contact. So, when there's motion, the two pins will act like a closed switch. When everything is still, the switch is open. Great for basic projects and wearables!
We also have a version with a slightly stiffer spring which makes it harder to trigger, and a version with a much more stiff spring which is even harder to trigger!