Major congrats to Michael Chen for winning the James Dyson Award for his Reactiv cycling jacket.
The jacket incorporates an accelerometer and LEDs to inform others of increasing or decreasing speed and, lift an arm, to indicate a turn with amber LEDs in the forearms.
When you pedal harder to speed up, the LEDs on the back light up green to indicate acceleration. Braking will change the green to red to indicate braking.
What an awesome and brilliant idea.
The other entries on the James Dyson site are also worth a look too.
Found via Bicycling Design where one of the commenters mentions microfiber nanogenerators to make power just during the natural course of movement. And that would totally kickass.