A friend of mine was traveling through various airports in the states. He had accidentally left his pencil bag in his back pack which had a pair of scissors in it. The scissors were over the length allowed on a plaine (Something like 4" is considered safe.)
He went through 2 security checks in the states, and boarded planes with these scissors in his back pack. It wasn't until he went through a simple, small security check in a small Canadian air port that they were found and confiscated.
I find it funny that he made it through all this elaborate security in the States, and a simple security check in Canada with a Security guard who did his job well found the scissors.
I saw exactly the same thing happen on Grand Cayman. At the end of the summer, Cayman Islands security found a pair of scissors in a girl's backpack that she'd evidently been traveling with all summer.
I wish I could remember the source where someone determined the most confiscated items by looking at the government auctions. The TSA likes to issue self-promoting press releases like, "we confiscated over 300,000 prohibited items last year," but it turns out they're primarily bottled water, snow globes, and Swiss Army knives.
Incidentally, states sell confiscated items at auction.
It was in my pocket. I walked through a metal detector. It was just a matter of the detector not being calibrated correctly or not being set to an adequately high sensitivity setting. That such things are possible is a testament to the uselessness of the system, if they can't manage to promulgate standards and procedures sufficient for the proper operation of a metal detector what hope is there that any other equipment is being operated correctly?