I have had SSSS once. I extended my stay – I was supposed to fly home let’s say Thursday night, but Thursday morning I changed my tickets so I would fly home Friday night. When I checked in I was specifically told by the checkin agent that the change was the reason for the SSSS – I was taking a flight I had booked the previous day. She, and everyone else involved, kept apologizing and explaining. I went through a separate security line, diverted there by the “look at your passport” person you go through first in US airports. This was actually a feature since I got whisked to the front. Then I stood in the middle of a big open space (other passengers kind of stared at me, which I didn’t like) while someone searched my carry-on reasonably thoroughly – I’ve had more thorough seaches post x-ray – and confiscated my face lotion.
On subsequent trips I didn’t get it again, lending credence to the “last minute change” explanation. BTW I have heard for folks who got it randomly, reprinting their boarding passes at a kiosk resulted in an SSSS-free boarding pass. I haven’t tried that myself and I don’t know that I would bother – it was probably a net benefit to have had the special treatment (though that face lotion had been through lots of screenings before and was never confiscated.)
Just had another SSSS and decided to update this answer. There were several changes this time around, some of which may have been about time passing, and some because this was in YYZ and the other in SEA:
I think this one was triggered by flying home from LAS landing at 6am, and then turning right around to go YYZ-SEA less than 12 hours later on a different airline, when I live here. That is a YYZ-LAS-YYZ trip smucked right up against a YYZ-SEA-YYZ trip. Also this YYZ-SEA trip was bought on relatively short notice (a few weeks.)
An acronym for ‘Secondary Security Screening Selection’ or ‘Secondary Security Screening Selectee’ which is an airport security measure in the United States and Canada which selects passengers for additional inspection
Though there is no published criteria how passengers are selected for SSSS, Wiki page lists few probable ones.
Actually this one may be fairly simple: From Wikipedia. You’ve been selected for secondary Security Screening.
Credit:stackoverflow.com‘