The metal oxide coating California's "Cool Cars" regulation mandates car windows starting in 2010 to not just reflect sunlight — it also bounces the signals for mobile phones, GPS navigators and, um, parolees' ankle bracelet, making reception noticeably crappier.
Which, I suppose, is one way to kill two birds with a single government-tossed stone: people won't be texting while driving because they can't get a decent signal anywhere, and cars will have a smaller carbon footprint since they won't get as hot. The whole GPS navigators sucking and not being able to accurately track parolees is a different problem for a different day, really.
The car manufacturers, for their part, would prefer a coating that absorbs energy, instead of reflects it, which they say would leave wireless signals unmangled, but I bet slightly warmer. [Detroit News via TUAW]