Emergency Brake Flash: Delivering 200 lumens of ultra-bright output with a high-efficiency optical lens for a wide 220 degree beam angle. Built-in 3D motion sensor boosts brightness to 300 lumens when braking, ensuring visibility range up to 1000 meters. Professional grade safety for every ride! Lightweight & Durable Design: Made with a PC optical lens + aluminum alloy housing. Includes a nylon mount for seatpost mounting only. Compact size: 1.57" diameter, 1.34" length, and just 0.1 Ib weight. Rated IP66 for waterproof & dustproof performance—ready for heavy rain. 4 Lighting Modes & Dual Buttons: Features slow flash, pulse, fast flash, and steady modes, controlled by two buttons. Short-press the power button to cycle modes; Short-press the brightness button to adjust light intensity (8 levels available). Long-press the power button to turn off, and it will automatically restore your last-used lighting mode and brightness upon next startup. Battery Indicator & USB-C Charging: Equipped with an 800mAh lithium battery (USB-C 5V charging). LED indicator lights up during charging and turns off when fully charged (about 3 hours). A full charge delivers 3-300 hours of runtime. On startup, brightness will pulse twice if battery is below 50%, or three times if below 25%. Auto Mode: Slow flash and pulse modes include smart programming to detect ambient light and motion, auto-off in daylight and auto-on at night. If idle for 30 seconds at night, the light shuts off but reactivates when riding resumes. (This auto feature cannot be disabled. you can choose fast flash and steady modes as a daily riding choice.) High Lumen Bike Tail Light Ultra Bright Compact Bicycle Rear Light for Night Riding