Commonly available glow-in-the-dark materials are made from phosphors, which are chemicals like zinc sulfide or strontium aluminate, that manufacturers mix with paint or plastics. These phosphors absorb energy from sunlight or even artificial light, then give it off over time; that process, known as phosphorescence, is what causes them to glow. For some objects, it is not desirable to rely on phosphors, since they need to be "charged" (i.e. regularly exposed to light in order to produce their glowing powers). For example, there are gunsights and watch faces made with tritium, a radioactive isotope of hydrogen, which glows continuously. The radioactivity emitted by a tritium gunsight or watch face is so weak that it cannot penetrate human skin, thus is deemed to be safe; manufacturers are quick to point out that you encounter more radiation just walking around on our planet. TEC Accessories, an EDC gear company, sells this line of Isotope Tritium Fobs. These are glow-in-the-dark key fobs that, you guessed it, rely on tritium for that always-on glow. There is a bit of a catch: TEC Accessories can sell you the key fob--but they can't actually sell you the tritium. Tritium is illegal to sell in the U.S., where the company is based. Thus they've got an entire page on their website describing how to skirt U.S. laws to get your hands on the stuff. Once you've ordered and received your vial of tritium, you can pop it into their key fob, and off you go. You're probably wondering: Aren't radioactive materials dangerous? As with gunsights and watch faces, the answer is that it might be—if you ingested it or inhaled it. Contained within a vial that is inserted into a titanium key fob, you'd have to go to a lot of trouble to do either of those things.You'd also have to go to a lot of trouble to order tritium. But darn if these things don't look cool. The fobs run $14.50 to $80 a pop.