When I ride rarely does a vehicle sneak up on me without me knowing but when on more quieter back roads I tend to go into sight-seeing mode. When this happens I'm more distracted. Having a mirror helps immensely but without a mirror sometimes a car will catch me unaware. Usually this is not a big problem as most motorist will toot their horn if you are too far out into the road. Also keep in mind that after a vehicle has passed you they will still create noise. This noise helps mask the sound of approaching vehicles ( *noise produced by vehicles passing on the opposite side of the road has the same effect ). With noise all around you it becomes necessary to know which direction the noise is coming from. With that said I'm curious to know how the radar device reacts to vehicles going the opposite direction. So far no one has mentioned that. If cars passing the opposite way cause the device to light-up I really wouldn't want one.

Though mirrors can be bothersome sometimes I'm glad to have one. I'm still experimenting with head mounted mirrors and as such I feel I haven't found the perfect solution. This radar thing is interesting but I don't really know how useful it could be without actual using one. One thing I do know, there are times when I need to know "how far" approaching traffic is behind me. If out of range the radar thing isn't really going to give me the advance warning that I might want.