Reading this NYT article about radar to cover car blind spots, which describes a system that will trigger lights in the rearview-mirror when cars are in the blind-spot, reminded me of an old idea I had some time ago I called "Eyes in the back of your head."
The idea would be to wear a special collar while driving. This collar would contain small electrodes that could lightly stimulate the skin on the back of the neck. Perhaps just one row, but ideally a small 2-D image should be possible.
This would be connected to a camera, radar or sonar system pointing back from the vehicle. It would map where other vehicles are, and turn that into an image on the back of the neck.
Thus, as a car came up behind you and passed you, it would feel like something brushing the back of your neck on one side.
I was inspired to this by reading about a system for the blind that mapped a video camera image onto a 2000 pixel electrode map on the stomach. It was found that over time, the nerves would retrain and a sort of limited vision could develop. Might this have application in driving, or perhaps combat?