A magnet is attached to a spring that keeps it’s held back until another magnet draws it forward, connecting the two contacts.
Non elastic pieces are sewn to an elastic band. When the band is stretched, the contacts touch!
Temple Flex Switch
A hard frame suspends flexible cloth with a metallic contact on one side and a non metallic contact on the other. A second contact is placed over the first contact so when teeth are grit, the users temple flexes, pushing the two contacts together. Simple right?