Never tried radar and never will. Pfffft. 99% useless 99% of the time probably. If there's only 1 car or truck then my ears can figure out where they are in the lane to a couple inches I bet. But that's already too close to be dodging.
Part of my rides is 70 or 80 mph 4 lane freeways. WTH is radar going to tell me??
ALL you need is a big bar mirror like mine that's 99% awesome. The other 1% is when I don't look and maybe a wide load sneaks up. LOL.
I can see back 1/4 mile+ where I can see if they are moving over or slowing down or whatever. Then I use this to judge if an oncoming squeeze compels me to adjust my speed and or ride the last 3" of shoulder edge. Happens all the time on narrower shoulders with plenty of trucks. Then there's also I need to judge when to zip across merge out lanes in 5 second gaps. Yah it happens on my tours too.
Sometimes the shoulder is lumpy and I cheat in and out of the drive lane.
Try any of this with a fricking beep beep that's impossible to hear anyway. And no, my mirror has no jiggle, sagging may happen with older ones.
Battery lights on a tour bike?? Hilarious.