The Transportation Security Administration was under pressure to establish rules regarding airport body scanners, and well, the Department of Homeland Security's weighed in. Now the Advanced Imaging Technologies (AIT) using Automatic Target Recognition (ATR) will be mandatory in certain cases. Slashgear notes that prior to this the scanners were opt-in, and one could go through a contactless, non-imaging scan instead. That option will exist, but security agents can insist on mandatory screening "for some passengers." The argument the DHS gives (PDF) is that these scanners are more capable of detecting prohibited, non-metallic items that could be hidden under a few layers of clothing than a metal detector wand would be.