Originally Posted by
UshuaiaHammerfest
I think the random alarm makes a different alert than a standard "You've got metal!" alarm. I triggered a random alarm walking through the precheck lane at one point and the screener immediately called out "Male assist USP!" which they said means "unpredictable screening procedures."
The random alarm doesn't sound until after you've walked through the WTMD. Random alarms only sound on people who don't alarm, so it has to make sure you're all the way through before it can figure out if you're eligible for a random alarm. That's why it usually catches people off guard. I can't comment on whether or not it has a different sound because I didn't even hear it when I got my random alarm.