I'm not sure how quickly we're approaching a reality where anyone could know anything about anyone else if they just buy the right app, but, conceptually, it seems possible within our lifetimes. And our legal system still hasn't caught up to addressing privacy implications of 30-year-old technology like email...
...FAST scans, however, exceed the scope of the administrative search exception. Under this exception, the courts would employ a balancing test, weighing the governmental need for the search versus the invasion of personal privacy of the search, to determine whether FAST scans violate the Fourth Amendment. Although the government has an acute interest in protecting the nation's air transportation system against terrorism, FAST is not narrowly tailored to that interest because it cannot detect the presence or absence of weapons but instead detects merely a person's frame of mind. Further, the system is capable of detecting an enormous amount of the scannee's highly sensitive personal medical information, ranging from detection of arrhythmias and cardiovascular disease, to asthma and respiratory failures, physiological abnormalities, psychiatric conditions, or even a woman's stage in her ovulation cycle...