Getting checked by the TSA’s advanced-imaging technology used to be entirely optional. Those who refused a scan could instead receive a pat-down search. In fact, many observers thought the agency installed the 740 body scanners with an understanding that no one would be forced to use them, ever. 
But in December, TSA revised its rules, saying an “opt out” is no longer an option for certain passengers, resulting in travelers at more than 160 airports not being given the option to say ‘no’ to the full-body scan.
The decision (see the full document on DHS.gov) drew mixed reactions, however, according to a former safety director of the Federal Aviation Administration, this decision was based on security threat assessments and the need to use scanners when security conditions dictate, to protect the public.
