If a passenger sets off the metal detector, engages in suspicious behavior, or is listed on a watch list, secondary screening would be appropriate.

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It was harder, he said, on his eight-year-old daughter, who was forced to remove her skirt when visiting him (its studs set off a metal detector).

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The rest present them as a voluntary secondary security option in lieu of a pat-down, which is protocol for those who've repeatedly set off the metal detector or have been randomly selected for additional screening.

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