CatEye's Reflex Auto tail light is a new paradigm for cycling safety. Available in red , this light is the only produced with built in reflectors that exceed international standards (USA, Great Britain, Europe, and Japan.). Be seen from any angle and in any situation. The Reflex Auto provide the rider with greater than 180 degrees of visibility and provide safety both while the light is turned on and while functioning solely as a reflector. The Reflex Auto will automatically turn on whenever both darkness and motion are detected by the motion and light optic sensors. No more stopping on the bike path to double check that you've turned your tail light on - it's automatic! Choose your level of safety with 5 distinct light modes: constant, flashing, pulse, rapid, and long-life. Each light is powered by one high power center LED (with OpticubeTM lens technology) and four 5mm LEDs that provide up to 120 hours of life on 2 AA batteries. Specifications Dimension: 81.4 X 44.3 X 30.3mm Weight: approx 82 grams (with bracket and batteries? Light source: Red LED X5 Battery: AAA alkaline battery X2 Runtime: Constant mode: 30hrs Flashing mode: 100hrs Rapid mode: 60hrs Long-life mode: 120hrs Pulse mode: 30hrs Mount size: dia.21.5 to 31.8mm *The factory-loaded battery life might be shorter than the specification above. *Design and specifications are subject to change without notice. Manual http://www.cateye.com/images/manual/ld570r_usa.pdf Video https://www.youtube.com/watch?v=jZ45gMmekI8&feature=youtu.be