Stay aware of approaching cars with the Varia RVR315. This rearview radar pairs with your Edge bike computer, smartphone or other Garmin device to alert you of vehicles approaching from behind up to 153 yards (140 meters) away. When used with your smartphone, the Garmin Varia app uses bold graphics to indicate the position and speed of approaching vehicles, plus tone and vibration alerts. The radar's compact vertical design allows for device mounting on most road-use bicycles. Ride more between charges with up to 8 hours of battery life.