"Any sufficiently advanced technology is indistinguishable from magic."
-- Clarke's Third Law (Arthur C. Clarke)
"Any technology distinguishable from magic is insufficiently advanced."
-- Gregory Benford's Corollary to Clarke's Third Law
We had our car towed to the local dealership of the city we broke down near. (See previous entry. Yes, back to back entries again. Sorry.) They've rented us a Ford Taurus in the meantime. I noticed that the rear-view mirror didn't have one of those little tabs to shift it to night-time mode so the headlights behind you weren't blinding. It did have what appeared to be a pair of some form of light sensors, but I didn't give them much thought. Behind the mirror was a box. At the time I saw it, I presumed it probably contained a GPS transmitter so the dealership could track the car.
As dusk was approaching, we were still on the road (with a long way to go). It was just getting to the point where I wanted to figure out what to do about the mirror when it took care of itself. Literally! As a car approached from behind with its headlights on, the mirror darkened! Since it was still fairly light, the effect was just subtle enough for me to wonder if I was imagining it or not. After another couple cars passed us, I knew I was not imagining it.
This is cool! And it truly appears to be magic. There are no visible moving parts. I have no idea how the mirror actually works. All I know is that in early evening, it will darken some as a car with headlights on comes by from behind. Once night has fallen, it will turn completely dark, reflecting only the headlights. It will lighten if there are no headlights close behind you, but by then it's so dark you can barely tell the difference.
It stirred a vague memory of reading or seeing something about this, but I think it was very long ago. And I had thought PDA's were science fiction come to life. I think this has those beat.