I saw a great line from Seinfeld the other night ... when George asked Jerry why he set off the airport scanner when he had no metal objects on him he replied "I must have iron-rich blood".
I found it strange that I never seemed to set those off even with some metal objects in my pocket. Maybe I have iron-poor blood. (C;
Of course, I haven't pushed my luck recently with the sensitivity cranked up a bit. But there was that time a few years back where I forgot I was wearing steel-toed shoes.