As of 2010, the Transportation Security Administration requires air travelers to remove their shoes when passing through airport security. As travelers pass through the metal detector gate, their shoes pass through the X-ray machine along with all bags and personal effects. The TSA has screened shoes, and demanded their removal, since 2006, when the U.S. security threat level was declared to be "Orange," or high. By screening shoes, anomalies such as bombs can be easily detected. Some airports, such as those of Madrid, Prague and Budapest, have adopted an alternative system of shoe screening whereby passengers do not need to remove their footwear.
Many acceptable items, such as keys, jewelry and mobile phones, may activate an airport metal detector. Therefore, passengers should remove all loose metal items from their pockets and place them in provided trays to pass through the X-ray machine. Items may include keys; loose change; cellular phones or PDAs; jewelry; and belts with metal components. There is a minor chance that clothing with small metal snaps or under-wire bras will also set off a metal detector, though generally such small amounts of metal are inconsequential. Body piercings may set off the metal detector depending upon their size. Travelers who set off metal detectors may be asked to submit to a full-body scan with a hand-held scanning device or a pat-down search by a same-sex TSA employee.
Airport metal detectors serve to ensure that no travelers board aircraft, or access the "sky-side" areas of airports, with certain prohibited items that may be dangerous to other passengers. Therefore, passengers are prohibited from carrying liquids of any class beyond a set volume. The TSA allows liquids to be carried in sealed containers of up to 3 fluid oz. each. All sealed containers must fit in one transparent, sealed quart-sized bag. Each traveler is restricted to carrying one such bag. While common lighters are prohibited in checked baggage, they may be passed through the X-ray in carry-on luggage, within the quart-sized bag. Scissors must measure less than 4 inches in length and must pass through the X-ray. Safety razors may pass through the X-ray, but other types of razors, such as loose razor blades, are not permitted.
