To date, the TSA has only approved two types of full-body scanners for checkpoint screening. As already mentioned, one is backscatter technology, which uses x-rays; the other employs active millimeter wave technology, which uses radio frequencies. The former is made by Rapiscan, the latter by L-3 Communications.
As of March, there were 379 active millimeter wave units and 247 backscatter units—or nearly 630 imaging technology units total—deployed at more than 150 U.S. airports nationwide, according to TSA spokesperson Kawika Riley. That number is set to double in the next few years.
In the past, both machines generated a naked image of the passenger; a remote screener examined the image for threats before signaling to the checkpoint screener that the passenger was clean. Even though the person seeing the image was removed from the actual person being screened, people objected to having a naked image captured.
To address that privacy concern, L-3 added a feature known as automated target recognition (ATR), which eliminates the naked body image. Instead, it uses advanced algorithms to analyze the scan, detect any potential threat, and display it on a gingerbread-man-like avatar on a screen attached to the machine. Because a naked image is never created, there is no need for persons to be remotely stationed to view them. It also eliminates concerns about whether images are being stored. Essentially, the privacy issue is removed from the equation. For that reason, for now, TSA is only buying the L-3 machines.