Garmin Varia - Cyclist Radar (car detection) for bicycles
Now this is cool... expensive but cool.
We are excited to announce the Varia line of smart cycling devices including, a first-of-its-kind rearview bike radar and smart bike lights. Helping create a safer cycling environment, Varia rearview bike radar warns cyclists of vehicles approaching from behind up to 140 meters (153 yards) and also warns approaching vehicles of a cyclist ahead, and Varia smart bike lights automatically adjust to changing conditions as well as the speed of the cyclist. Both the radar and lights work independently, or seamlessly integrate with each other and with compatible Edge cycling computers, allowing cyclists to customize to their needs.