accelerometer/motion sensor! These spring-vibration switches are medium sensitivity non-directional vibration induced trigger switches. Inside is a medium hardness 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 stiffer spring, which is harder to trigger, and a version with a very soft spring, which is easier to trigger!