“Sting” was, of course, Frodo’s sword in Lord of the Rings, which had the useful feature of glowing blue whenever orcs were in the vicinity. Conrad Gempf reports on an ingenious real-life counterpart: an umbrella that glows blue depending on how likely it is to rain.
How does it know? Well, depending on where you are on the poetic/literal continuum, it’s either elvish magic, lost in the mists of Middle Earth history; or else it’s WiFi technology cooked up by a couple of guys in Chicago. Your choice, but I know which I prefer to believe. 😉