The TSA scanners are presented to the public as a tool for detecting weapons and other contraband, but I think this is actually a secondary goal and a bit of misdirection. Think about what those scans actually are.<p>They&#x27;re biometrics. They take precise measurements of a person&#x27;s shape, which is sufficient to detect if someone is traveling under a false name, and they&#x27;re building a database of those biometrics to have available for use elsewhere. If the scan&#x27;s result is ambiguous, they swab your hands and stick the swab in a machine, supposedly to detect residue from explosives but with the nice side-effect of producing a stored DNA sample for later use. They&#x27;ve proven pretty useless for controlling the flow of contraband, but they&#x27;re quite useful for catching fugitives. While the people staffing the checkpoints aren&#x27;t particularly smart, it&#x27;s reasonable to assume that the people at the top are pretty clever, and their policies are consistent with this having been the real goal all along.<p>If they tried collecting fingerprints from travelers, they would get a very strong backlash. This way, they get a weaker backlash and some jokes about how stupid they are for using machines that can&#x27;t reliably detect guns.