When it comes to air travel, you might encounter a slew of unexpected delays - there could be technical issues with the plane or bad weather coming through, but there is one delay that you may encounter that you'll know about before it happens. That's because a code alerting you to it will be in plain sight on your boarding pass.
It's called Secondary Security Screening Selection and shows up as SSSS on your pass. It means that the TSA wants to have a chat with you about your travel plans and take a closer look at your ID and luggage. You'll also be treated to a full body pat-down and likely have to go through a metal detector and/or body scanner multiple times. In addition, you'll need to turn on any electronic devices for security.
Just when you think you are finished, you aren't - when you check in at the gate, an alarm goes off as your pass is scanned so the gate agent can ensure you've been properly examined.
So why does it happen? Well there is no official reason, but you tend to be more likely to wind up with the SSSS if you book a last minute flight, a one-way international fare, pay with cash or travel from what is considered a "high-risk country." Some people on watch lists might wind up with it, but really, anyone can get it on their pass since there is a random selection to who winds up with it as well.
If you do see an SSSS on your ticket, you will definitely need extra time to get to the gate so keep that in mind. You can also try going to a priority line at security and showing them your pass so you don't have to wait in a general security line only to be pulled out of it and inspected once you get to the front of it. If the agents are nice and not too busy, they might help you out.
Finally, don't think you can escape the SSSS delay with TSA PreCheck. Even those who use the service can get it and if they do, they can't use TSA PreCheck because of it.