[gchappel]

I use a garmin rtl510 radar. Gives a beep and tracks the cars behind you.
This works really really well, I was surprised.
I ride in a rural area, might have a car every 10-20minutes. This is not worth it if you are riding where cars are everywhere.
Still need a mirror, but this really helped me relax. When it says the coast is clear I know there are no cars sneaking up behind me.
Gary