Garmin Varia Rearview Radar Light Bundle APPROACHING VEHICLE INDICATION - The radar display unit (RDU) and compatible Edge cycling computers indicate up to 8 approaching vehicles from behind, giving the cyclist information about the distance and rate of approach. AUTOMATIC ADJUSTMENTS - The tail light brightens and blinks when approaching vehicles are detected for an extra measure of safety. Vehicles approaching from the rear is the number one cause of bike/vehicle fatalities in the U.S. THREAT LEVEL INDICATOR - Indicates the relative speed of approach and distance of one or more vehicles at a time. World's first cycling radar that warns of vehicles approaching from behind up to 153 yards (140 meters) Dimensions: Radar display unit: 2.4 x 1.3 x 0.7 (60.0 x 34.0 x 19.0 mm); Tail light: 2.9 x 1.7 x 0.9" (73.0 x 44.0 x 23.0 mm)