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