The guee aero x smart rear light this smart tail light comes with brake sensor technology the light will increase it39s flash rate and brightness under heavy braking or over bumpy roads which makes the rider more visible on the road designed with an adjustable wing the aero x can be mounted on both aero and round seatposts guee aero x smart rear light features super bright red led 37v li poly rechargeable battery mini usb charger supply 5v approx 2 hours 10 minutes approx