Brady Clark and Mykle Hansen made this nifty DIY speed vest for bikers that displays a light-up readout of the wearer’s speed. The vest works thanks to an Arduino open source computer, wheel speed sensor, nine-volt battery, and electroluminescent display. Hansen and Clark describe the speed vest as a “bicycle safety device and advocacy tool.” I don’t really see how this vest does all that. It does manage to make the wearer look like a tool though. I can’t imagine anyone actually wearing this, but the work these guys did to make it happen is still very impressive.