The LED Valve Stem Cap. Put one on your car, bike, ATV, or motorcycle. When the wheel rotates the LED turns on a strobe light using syntrifical force. So the LED only says on while the means of transport is in motion. The cap itself is Metal and comes in the following colors white, red, green, blue, yellow, ultra violet, and color changing RGB (3LEDs). Comes in 2 per package, with three (3) batteries OFF ROAD ONLY check your local laws to see if they are street legal.