LAS VEGAS -- How you act when traveling through an airport may give security yet another reason to screen you more carefully.

At select airports across the country -- possibly at McCarran Airport -- the Transportation Security Administration is using a new method called Behavior Detection to see which passengers raise red flags.

Plain-clothed officers trained to look out for particular signs of nervousness or behaviors that could be caused from uncertain motives will be monitoring airport crowds. If these officers feel a person is acting suspiciously, he or she will pull the traveler out of line to be questioned and searched.

"Passengers that look like they would be deceptive," said Tim Decker, TSA director at McCarran Airport. "The passengers who look like they were under a lot of anxiety or stress, or exhibit behaviors that are not normal (will be questioned)."

This process is currently taking place at a handful of major airports around the country. But the new tactic is raising alarm among groups like the ACLU, who fear it could lead to racial profiling and illegal arrests. Experts also said it's an easy system for terrorists to beat with very little training.

TSA has almost 2,000 agents trained on Behavior Detection Nationwide, and plans to train 600 more in the next year. Those new officers will head to different airports nationwide.