True gaming story: Long ago (roughly 2005, IIRC) our group was playing a Buffy the Vampire Slayer campaign and i proposed building a device based exactly on this sort of thing. A binocular watch camera, one arm of which included a mirror, while the other was pure refractive optics. Since it would have stopped the GM's so-called plot in its tracks, he stonewalled it, even after I pointed to available off-the-shelf optics and gave URL pointers to astronomy image analysis software that would be able to do the almost-real-time image comparisons for detection of vampires.