1. ARC-P: tough and reliable. Always-there handy. Probably access it a dozen times a day.
2. On a standard STEEL BEAD CHAIN...
... just like the U.S. military has been issuing I.D. dog-tags with since WWII. It's durable, but SAFE -- because it'll snap if you/it get seriously snagged in some dangerous machinery... or if you foolishly allow some, umm, socially-disadvantaged Mugger to get bad-breath close and grab it before you put a .45 ACP hollow-point in his boiler-room. Costs about $3 for a 28-inch length at hardware stores. Won't snag chest hair like some "jewelry" nor will it absorb sweat and stink like nylon cord. Clean and simple, suggesting a no-bull present/past military connection that makes sheeple-weenies wet their panties. Definitely not for Look-At-My-Gold-Chains/Disco-Gigolo types. YMMV.
I wear mine under a shirt, though around the house I often wear it "out" for quick accessability. Especially handy when reading prissy-print menus in dimly-lit restaurants... or when grilling steaks in the yard on dark nights. Invaluable if you ever get stuck in a hi-rise building's elevator during a power-outage, earthquake, etc. BT/DT (twice).
Energizer L92 lithium AAA batts also make it a tad lighter (weight), brighter, and more comfortable than alkalines.