#9 Solar Bike Odometer
Number two for pedal-powered bikers: the Solar Powered Bicycle Odometer. It looks a bit like an old solar calculator, given the tiny solar panel powering it, but has even fewer buttons. Keep track of current speed, fastest speed, average speed, distance travelled and calories burned, among others. It is also equipped with a 12- or 24-hour clock and measures only 3x2x0.5 inches—very small and easy on the handlebars.