Airport body scanners detect metallic and nonmetallic threat items, like bombs and knives. They also identify benign undivested items, like keys, coins, jewelry, IDs and phones. But there are plenty of other items that can set off the scanners — including thick hair, especially if it's in a bun or braid and there are clips holding it back, and wire supports for undergarments. Even some tumors might trigger the machine, but only growths on the outside of your body (like fibroids) will cause a red signal.
In general, the machines have a hard time detecting low-density materials such as gels and liquids. So while they might pick up the sheet explosive that Abdulmutallab tried to use on Christmas Day, it's unlikely they would have detected his smaller bomb, which he kept in his underwear.
If the electromagnetic waves hit something suspect, a TSA officer might check it manually or ask you to step aside for a pat-down. But if nothing stands out, you should be allowed to continue on your way. To get a better idea of how you might beat a body scanner, we asked a handful of security experts. Their answers may surprise you.
