Hand Crank Generator
The end of the crank that is inside the body of the device is covered in magnets. Around that is a little dead air space and then a ton of coiled wires. When you crank the generator, it spins the magnets creating a magnetic field. The magnetic field a current of electricity in the coiled wired. If it's a hand crank generator, the electricity is then stored in a bunch of capacitors or batteries.