This topic has been covered with truly excruciating detail here in the past, as well as our interpretations of the NRA regulations regarding them.
You should be able to turn up a LOT of threads here with some searching. The best on with some actual math trying to calculate the doses involved is
HERE but make sure to read further than just the actual post I linked to as there is alot of extra information.
The point to take away is that a glow ring is almost completely harmless /ubbthreads/images/graemlins/wink.gif With the right equipment you can actually measure some radiation outside the case, but it won't make it through the fabric of your pocket much less through your skin into your reproducing bits. If you eat them and absorb the tritium you still wont get hurt.
The reason they are illegal in the US is not because any single or multiple ones you might own will cause any problem, but because our government is worried about millions of them showing up in landfills. They don't consider a key fob to be a usage of tritium that is worth the potential clean up costs. Most of us around here consider that to be silly, but have yet to run for office on the platform of reforming the NRA /ubbthreads/images/graemlins/smile.gif
