In March, the Transportation Safety Administration began to deploy dozens of new full-body scanners at select airports, with plans to install a total of 450 of these units during 2010. Frequent business travelers are likely to encounter this high-tech, hands-free version of a pat down soon. The new scanners can detect items, such as nonmetallic weapons and explosives, which can be missed by metal detectors. Here’s what you need to know:

There are two kinds of full-body scanners: some use millimeter wave technology and some use backscatter technology.

Millimeter wave machines direct radio waves around your body and measure the energy reflected back to create a three-dimensional image. They reveal explosives if they are denser than other materials. They emit radiation, but in amounts less than that of a typical cell phone, according to the TSA. This type of scanner produces an image that looks something like a fuzzy photo negative – the body’s contours are visible, but specific features are not clear.

Backscatter machines are low-level X-ray machines that produce two-dimensional images. They emit about as much radiation as you are exposed to in just two minutes of flying in an airplane. This type of scanner produces an image that looks something like a chalk etching.

The images produced by the scanners are not viewed by personnel at the security checkpoint. Instead, the images are transmitted to a security officer in a remote, secure location. This officer inspects the images and communicates via wireless headset with the personnel at the security checkpoint. After you are cleared, your images are automatically deleted from the viewing system, which has no storage capability.

Passengers with heart pacemakers and surgically replaced body parts, such as metallic hips and knees, can safely pass through the new machines.

Being screened in a full-body scanner is optional – you can choose to have a physical pat down instead. However, initial reaction to the new scanners is positive – the TSA says 98 percent of passengers who encountered the technology during TSA pilots prefer it over other screening options. Airports that now have full-body scanners include Atlanta, Baltimore/Washington, Boston, Chicago, Dallas/Fort Worth, Denver, Detroit, Las Vegas, Los Angeles, Miami, Phoenix, San Francisco, Tampa and Washington D.C.