Radioactivity in Watches: any Info?

I once heard that some watches (particularly some military style
thingies which are supposed to glow nicely in the dark) use some
certain radioactive substances (probably tritium or radioactive
promethium) to permanently excite the phospors (or something like
that) and make them glow indefinitely in the dark. I realize that
serious precautions must have been taken by everyone involved to make
sure that any possible danger is minimal or nonexistent. Nonetheless,
I am a bit curious with this matter. Does anyone know where to find
more info, say on which brands / models use such an approach, and how
serious the health hazard really is, if at all it is real? Cheers, Jos