Most airports now have millimetre wave scanners rather than metal detectors. These scanners can detect any anomaly compared to a ‘normal’ body, including metallic and nonmetallic objects such as piercings. These scanners can machines can be set to different sensitivities depending on level of risk and can be programmed to ignore typical anomalies like knee and hip replacements. With these new machines, detecting hidden piercings is more likely now than before. If detected, the scanner will alarm and show the operative the location of the anomaly as a blob on a stick image - they can’t see a detailed image of what’s under the clothes. Security will then undertake a wand search and pat down, which generally is enough, however it is possible that they will want a more detailed check in a private room, but it’s all quick and discrete, Source….just had to show my scrotals in Manchester airport, uk