There are now a number of ebikes equipped with radar systems which warn riders of vehicles approaching from behind. If your bike isn't among those, you can now change that by slapping on Garmin's Varia eRTL615 radar/tail light module.
Garmin unveils Varia eRTL615, its first rearview radar designed for your eBike
Garmin Varia™ eRTL615, Bike Radar
garmin varia
Garmin Support, Varia™ eRTL615
Garmin Support, Varia™ eRTL615
Garmin Varia™ eRTL615, Bike Radar
Garmin Support, Varia™ eRTL615
Garmin releases e-bike specific Varia rearview radar and tail light - BikeBiz
Garmin Varia eRTL615 eBike Rearview Battery-Free Radar with Wearable4U E-Bank Bundle : Electronics