And note that breathing into your hand to try and detect it does not work (it's like using a mercury thermometer to measure the temperature of its own mercury).
What does work is licking the back of your hand (a good Gene Simmons all-over-tongue job, not just a tip-tickle), waiting ten seconds or so for it to dry, and then sniffing it.
Sounds gross? I guess that depends on what you've been doing with your hand...