I have a metal rod in my back that is substantial enough to set off metal detectors.
Last year, I was planning my first flight since 9/11 and I was in utter dread because... how do you prove you have a rod in your back? I didn't want to be strip searched or patted down or x-rayed or anything else.
I set off the alarms BOTH ways -- coming and going.
In each case, security waved me through (I'm white, female, and utterly non-threatening looking to your Average American Male) and stopped the person BEHIND me. In the first case, they made the person take off their tiny stud earrings and "go through again"; in the second case, the guy fished around in his pocket and found something to satisfy them that "must" have set off the sensors.
I felt bad for the people behind me, but since it was solved so quickly in each case, I didn't fess up and say that it was me that set the alarm off.