Light Up Wrist Ball
This tennis ball size gadget works via a ball within a ball system creating immense gyroscopic force, with speeds recorded of up to 15,000 rpm and generating a force of up to 40lbs. No batteries required, just wind the thread around the ball and pull briskly to get the ball in motion. The faster it spins the brighter the built-in light gets. Apparently great for the rehabilitation from carpal tunnel syndrome and RSI. Apart from the more serious side the wrist ball is an addictive plaything for all ages.