This is pretty interesting. A company in Munich, Reevu, built a helmet that allows piki piki (motorcycle) riders to see behind them.
Reevu spent ten years developing the helmet, which has a built-in 180 degree unbreakable rear-view mirror system in the hope it will save lives on the roads by improving situational awareness and hence preventing accidents. The innovative technology allows the wearer to see the road behind, using a system of unbreakable mirrors constructed out of ABS, which are contained inside the helmet shell and provide a window in the top of the helmet opening – a robust, low cost heads-up display. (from Gizmag)
I’d like to try one of these on to see how they actually work. It seems that your sitting position, and the type of bike you’re riding, would call for an adjustment. I’m also interested in what the price tag will be (they’re saying $399, but I’d be surprised if that’s what it actually goes for).