Varia RearVue 820 is the rearview radar and tail light that alerts you to approaching vehicles on your compatible Edge cycling computer, Garmin smartwatch or Varia app on your smartphone. With our most powerful and precise radar tracking technology, it detects vehicle size and threat level with a wider field of view. The radar tracking technology identifies vehicles that are following cyclists at the same speed or attempting to pass (same-speed tracking is limited or may be unavailable at slower speeds or when the radar cannot detect the road because of weather conditions or obstructions). The tail light is visible from up to 2 km (1.24 miles) away and has a unique brake light flash pattern to alert other road users when you’re slowing down or stopping. For peace of mind and awareness on the longest of rides, get up to 24 hours of battery life in day flash mode and up to 30 hours of battery life in radar-only mode.