As someone who's very well-versed in the art of piercing, I get asked this question a lot—usually by those who don’t want their precious piercings to be discovered. For instance, if you’re going to an airport, sports game, or any other event where a metal detector could be, you might wonder if you’re going to end up setting off all the bells and whistles.
Before answering the actual question, it'll be helpful to understand how metal detectors work and the reasons they're used for security purposes. A metal detector emits an electro-magnetic field that flows until it comes across something metallic. The metal object disrupts this flow in different ways—depending on its size and the type of metal—and is designed to give an audible signal when the field is disturbed.
Security metal detectors, like the ones posted up at every airport, are used to look for dangerous objects like knives, guns, explosives, and other weapons that could threaten people's safety on a flight. Adjustments can be made to the metal detector to determine how sensitive it is based on the level of security needed. For example, if necessary, a metal detector might be set to detect just a very small amount of metal.
If metal detectors are set be over-sensitive, it can result in false alarms triggered by harmless metals. If this was always the case, areas at large public events such as concerts and sports games would be completely congested with people setting off the alarms with everything from keys to jewelry to pens. Needless to say, it would make the job of actually finding threatening objects close to impossible. It's for this reason that most metal detectors are generally not put on a high alert setting.
During my most recent trip through airport security, which was extremely tight with its rules about liquids and how many personal items you could carry on, my eight piercings didn't cause any issues walking through the metal detector. What's more: Neither did my underwire bra. However, the penny I failed to remove from my pocket was caught by both the walk-through and the wand. The wand also reacted to the metal buttons on my jeans, but not my piercings.
In general, a few piercings usually does not pose a threat of setting off an alarm. However, with today’s heightened security, it is always a possibility. The risk also increases with the more piercings you have, or if you wear larger jewelry like hoops or gauges.
All this to say: If you really don’t want to have to explain your piercings, we'd recommend removing your jewelry beforehand to avoid the situation altogether.
*If your piercing is new (less than 6 months) it is really not recommended that you remove your jewelry unless absolutely necessary. Even a healed piercing can close up quickly and make replacing the jewelry difficult and painful. Since your chances of setting off the metal detector are very slim, it might be best to just risk it. However, if setting off an alarm could cause serious problems for whatever reason, and removing the jewelry is your only option, please let a professional help you put them back in.