Paul,
I fear you have been pipped to the post. The jewellery which you are
describing is already in use by the Tamil Tigers, Sri Lanka’s Tamil
militia fighting for a break away homeland (or terrorists, depending
on which side of the fence one is standing - it has been a long and
messy confrontation). I believe the content is cyanide and the
ampoule is made of glass, so that when you chomp down the poison
entering the cuts in your mouth kills you faster than simply
ingesting it. I think the string that the ampoule is on is also
colour coded to denote rank or status of some sort, but I may be
wrong, and wearing it is a symbol of commitment - which makes sense
when you think about it.