The Dealextreme Tritium Glowrings are actually way to expensive.

In the UK, the equivalent DX model for $35 is available here for about $14. They make for excellent kit markers in the dark.

http://www.amazon.co.uk/Nite-glow-keyring-illuminates-colour/dp/B000EXZNA0/ref=cm_cr_pr_pb_t

The tritium glowrings don't register above background radiation levels.

http://www.youtube.com/watch?v=Kmf7uyncw9E

I think that DX are charging a premium for these due to the difficulties of importing them into the US from other sources.