I have no inside information on the following... but an effective explosive trace detection screen would go like this. First, it would be random, with no profi

I have no inside information on the following... but an effective explosive trace detection screen would go like this. First, it would be random, with no profiling. Profiling gets defeated by shaving, change of clothing, etc. Random selection can't be defeated. I would make it resistant to implicit profiling from the operators by saying "wear a watch, every time the seconds reach 0 you select the next person for screening." Then, I would make it hard to dodge being selected by varying pace through screening, with a rule that "at the selection time you pick the next person through the metal detector, without giving passengers any indication that you've picked, and wait for your selectee who gets screened no matter how much they dawdle or how long the X-ray search takes". Next time you fly you'll observe that the ETD procedure at Australian airports is consistent with this theoretical design.