The Reflex Auto will automatically turn on whenever both darkness and motion are detected by the motion and light optic sensors, providing the rider safety both while the light is turned on and while functioning solely as a reflector. Specification 5 LEDs Greater than 180 degree visibility Automatically turns on / off by light and motion sensors Emits light for 50 seconds after the bike stops Built-in reflectors that meets highest government standards (USA, Great Britain, Europe and Japan) OptiCube lens technology AAA alkaline battery x 2 5 modes Mode memory function SP-5 bracket (ø21.5-31.8mm) and Rear rack bracket 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: f21.5~31.8mm Colour: BLACK