Two-pack Safety Tire Strobes with included Presta valve adaptors keep you visible when riding. Simply screw the Safety Tire Strobes onto bicycle's valve stems and you're ready to go! The motion-activated red LEDs automatically light-up with a bright, flashing strobe. The constant motion of your wheel creates a red ring of light around your rim. The red LEDs will automatically turn off after several seconds when not in motion. Use the included Presta valve adaptors for Dunlap or Presta vlaves. If your bicycle uses traditional Schrader valves, unscrew the Presta valve adaptors before installing.