CAT EYE - TL-AU165 Rear Bike Light with SP-5 Clamp BE SEEN: The flashing LEDs alert others of your presence, keeping you safe in low-light conditions. ONLY ON WHEN YOU NEED IT: The light detects darkness and motion and turns on automatically and continues flashing as long as the bike is in low light and moving. The light automatically turns off after a minute of no movement. GO THE DISTANCE: With a battery that lasts up to six months, you can install it and forget about it. SECURE ATTACHMENT: The TL-AU165 comes with the SP-5 clamp which fits bars or seat posts 25.4 to 27.2 mm in diameter. ALL WEATHER PROTECTION: Don't let a little rain stop you from riding. Your CatEye safety light is approved to work in all weather conditions.