If you like to ride your bike at night you know that visibility to motorists is extremely important. For around $US50 of materials and a little electronics experience you can add turn signal LEDs to any jacket or sweatshirt.
Instructables user leahbuechley (Dr. Leah Buechley) used this device to test out her Lilypad — an Arduino designed for wearables and e-textiles. In this use the Lilypad powers a set of left and right turn LEDs as well as power and switch indicator LEDs on the jacket.
To do this modification yourself you'll need a LilyPad Arduino board, an FTDI connector, power supply, LED lights, two push-button switches, conductive thread and general hand sewing gear such as scissors, fabric glue, needles and a fabric marker. You'll sew the LilyPad, FTDI, and power supply and test the circuits before adding the lights and sealing the electronics. You'll then program the LilyPad, plug in the battery pack, and go biking. The jacket is hand washable (after you've removed the battery back naturally).
Turn SIgnal Biking Jacket [Instructables]