Detects when you are breaking to emit a bright light alerting others you're stopping. Max 75 lumens / 19.5 hour runtime in Flash mode. New 400 mAh battery. Larger battery, longer runtimes. Wide angle optics with 270° visibility for maximum safety. Aero and round seatpost compatible. Lightweight and durable. IPX7 water resistant co-molded design Lezyne Bicycle Cycling KTV Pro Alert Drive Rear Black Led Lighting