The ROCKBROS TT30-WD is a compact red LED rear light designed primarily for bicycle helmets, though it can also be attached to a seatpost. Weighing only 20 g and measuring 40 x 30 x 20 mm, this plastic light clips easily into helmet ventilation slots to keep you visible from behind. It provides 20 lumens of brightness across five different lighting modes, including constant, rotating, breathing flash, and both quick and slow flash options. The device is powered by a 220mAh USB rechargeable battery that you can top up using a laptop, power bank, or standard charger plug. Because it is waterproof, you can rely on it during rainy rides without worrying about the electronics.