They show their badge and they're through.
Many of the captains are armed (you never know who) so they never go through the magnetometers... and remember the stink a few years ago about the crews having to go through those millimeter-wave x-rays
several times a day sometimes and how nobody really (even yet) knows what kind of damage those things cause the body... so they are excused from scans completely.
I think some airports use the biometrics on their badges, and some don't, but unless you're a muzzie convert after the fact, once you're in the system you're in.