Originally Posted by
exerda
This has unfortunately been the case at all Pre WTMDs for some time (years). What TSA varies is the rate of "random" rejections: it had been fairly low IME of late, but I've had bad stretches where it "randomly" rejected me for several flights in a row.
You can usually tell the difference when walking through: a metal detection beeps right away, whereas the "random" one beeps a half second or so later. (It also IIRC shows "RAND" or something similar on the LED display atop the WTMD.)
In the past, this meant just a hand swab and possible bag secondary--annoying, but no big deal as it resolved in seconds. Earlier this year, they went to directing all WTMD alarms to the Nude-o-Scopes, which I find more annoying.
He was unfortunately right.
You're spot-on with everything, except that TSA no longer calls it "random selection." They dropped the pretense that it's random. It's now called a "quota," because they have a set quota of additional screening selections per day.
So, you will hear the TSO refer to it as a "quota," or a "quota alarm." In airports where AIT scanners are installed in the pre-check lanes, the quota selectee will be sent to the scanner. In airports where there are no scanners in the pre-check lane, the quota selectee will get, at minimum, a hand swab for explosives.