Garmin Varia Radar RVR315

Varia RVR515 is a smartphone compatible cycling radar and 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
Compact vertical design mounts easily to most road-use bicycles
Battery life: up to 7 hours