WASHINGTON, Feb. 17 (Xinhua) -- U.S. aviation security authorities will begin using portable screeners at airports to check for explosives from passengers and their carry-on bags, the USA TODAY reported on Wednesday.

Sterling Payne, spokeswoman of U.S. Transportation Security Administration (TSA), said that the portable machines have already been tested at five airports after the failed Christmas bombing attempts and will be rolled out nationwide in a few weeks.

The explosives detectors are usually fixed at airport checkpoints. Screeners take chemical swabs from passengers and their bags to check for explosives under sensors, which are so sensitive that even passengers who have recently taken heart pills containing nitroglycerin can ring the alarm.

It marks the first time that explosives screeners, whose size is like a microwave oven, will be used outside checkpoints. Screeners can use those machines to take random checks on passengers waiting in lines for boarding an airplane.

The new explosives screeners will fill the security hole under current metal detectors widely used at all airports. Those metal detectors can not spot materials such as the powdered explosives that a Nigerian used to destroy a U.S.-bound airliner on Dec. 25.

The TSA reinforced security measures at airports immediately after the near-disaster Christmas Day bombing plot. It ordered passengers from 14 countries to be subject to extra security checks including full-body scans, which has stirred strong opposition from human rights activists for infringement of privacy.