. . . I've been wearing the same mini Fox 40 on a chain on my neck for at least five years. Still really loud and no problems.
I don't wear it on my key ring though. Things on my key ring get too beat up. Screwed up a good mini squeeze light that way.
HJ
I have a steel whistle on my key ring because it is bulletproof -- heavy, but close to indestructible. The louder, bulkier but not quite indestructible (polycarbonate/co-molded elastomer) Fox 40 Sharx stays in the back-pack.