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 releases Varia rearview radar specifically for e-bike use
Garmin combines tail light and radar in new Varia eRTL615
Battery-free 24 GHz rearview radar and tail light for compatible eBikes (requires compatible Garmin eBike cable; sold separately) Radar detects
Garmin Varia eRTL615, Rearview Radar and Tail Light, Powered by Your Compatible eBike, Visibility up to 1 Mile Away
Garmin unveils Varia eRTL615 a rearview radar for your eBike
IN THE BOX: 1x Garmin Varia eRTL615 (direct rack mount), 1x 2-bolt to friction flange mount adapter, 1x seat rail mounting kit, 1x Wearable4U E-Bank,
Garmin Varia eRTL615 eBike Rearview Battery-Free Radar with Wearable4U E-Bank Bundle
Garmin Varia eRTL615 eBike Rearview Battery-Free Radar with Wearable4U E-Bank Bundle : Electronics
Garmin Varia eRTL615 Radar for E-Bikes - Bike Shop Girl
New E-Bike-Specific Rear Radar Light From Garmin Is Here
Garmin Varia eRTL615, Rearview Radar and Tail Light, Powered by Your Compatible eBike, Visibility up to 1 Mile Away : Electronics
New E-Bike-Specific Rear Radar Light From Garmin Is Here