Using a cell phone while biking can be a disaster, but navigating the new system of Citi Bike stations can be a tempting reason to pull up a map as you ride. This helmet design from Adafruit Industries solves that problem with lights that can direct you to the nearest station.
The project uses Adafruit's FLORA GPS to communicate turns with flashing lights. The light-up helmet also increases your visibility for biking at night.
The full DIY instructions are available here, including a wiring diagram and a downloadable code.