The unique & versatile TEC-S311T Isotope Tandem Fob is designed around the use of a glass tritium vial (not included), which will glow continuously for many years without needing to charge it from sunlight or UV light. Similar to the TEC-S323 and TEC-S360 models, the shorter profile and dual split ring holes at each end of the Tandem Fob will add a subtle touch of luminous style to your keychain or it can give your favorite gear it's own special glow. The Isotope Tandem is an economical way to add a functional glow to anything you attach it to.You can also change out the vial anytime you like for different glow colors. Use different colors to identify different pieces of gear! Complete your EDC collection with the small, functional and stylish TEC-S311T Isotope Tandem Fob, which provides just the right amount of light for locating items in the dark. Clip it between a backpack zipper and flashlight. Try it out with a P-7 clip and your best pocket tool. Attach it between the pull chain and pull knob on a ceiling fan.