I just recently got back from a flight to Pittsburgh, and got caught by security. It puzzles me though that I didn’t get so much as a beep out of the checkpoint at Detroit, and I was wearing the EXACT same clothing and jewelry that I was a week later in Pittsburgh. Then, when the lady went over me, the detector went off at each of my peices of jewelry, but nor my belly button. It also went off on my shoes. I was wondering why it did that, with my shoes, not my belly, and only at Pitt, and not Det?
Detectors can bet set to alert at different sensitivity levels. Normally small pieces of jewlery or coins won’t set them off, but post-911 many airports probably set them lower.
This is a slight hijack, but I didn’t think it was worth its own thread: I got my belly-button pierced in November, but haven’t flown since then. Will this cause metal detectors to go off?
Probably not, if that’s all the metal in your body. Walk-through metal detectors generally aren’t that sensitive, otherwise no one with fillings could get through without…wait for it…
…a cavity search.
Sometimes I’ve had to take off earrings for metal detectors, sometimes they let me go through with jewelry on and it doesn’t go off.
Some years back (pre-9/11) I went to an airport with my uncle and cousin to pick up another uncle who was flying in. We were allowed to go right to the gate, but we had to go through the metal detector first. My cousin the spike-collared metal-goth had a lot of trouble remembering all of the places he was wearing metal… eventually they gave up and let us go through. 
Good stuff!
Don’t forget that shoes often use metal nails to attach the body of the heel to the shoe. If your belly jewelry was silver the skinny little belly button ring may not have had enough metal to trip the detector.
If you’re really concerned about what will or won’t set off the detector, just play it safe and don’t wear any jewelry. I don’t know anyone who’se ever met their SO on a plane, so dressing to impress isn’t really an issue (unless, possibly, you were going straight to an important meeting of some kind).
Vancouver airport always catches my replacement shoulder joint (a big chunk of metal!), but Dallas-Fort Worth never does.
Strange, I think.
I used to fly a lot. Different airports seem to be set at different levels. Sometimes I’ll make it through with my watch on, sometimes anything at all will cause the alarm. They once found a dime in my pocket after wanding me because I didn’t pass the detector. They all seem to be more sensetive lately.
Shoes, by the way sometimes have metal shanks. This sets off the detector.