Garmin's Varia product line does this. https://www.garmin.com/en-US/c/sports-fitness/cycling-bike-computers-bike-radar-power-meter-headlights/?series=BRAND1056

Garmin's Varia product line does this. https://www.garmin.com/en-US/c/sports-fitness/cycling-bike-computers-bike-radar-power-meter-headlights/?series=BRAND10561 https://www.garmin.com/en-US/c/sports-fitness/cycling-bike-c... I do prefer a decent mirror though. Radar can't tell me what a car is doing, what it is, if a bicyclist is approaching, if my friend stopped to fix a flat, etc.