Varia rtl515 is a smartphone compatible cycling radar and tail light rearview radar with tail light provides awareness of vehicles approaching from behind up to 140 metres away pairs seamlessly with your edge bike computer and compatible smartphone as well as select garmin wearables or the radar display unit when used with your compatible smartphone, the varia app provides graphics plus tone and vibration alerts that indicate approaching cars when used with a compatible smartphone, varia radar integrates with third party apps such as ride with gps to overlay your maps with rearview radar alerts daylight visibility up to 1 mile alerts motorists to your presence as soon as possible compact vertical design mounts easily to most road use bicycles peloton mode provides a low intensity light flash that is perfect for cycling in groups battery life up to 16 hours in day flash mode, up to 6 hours in solid mode