You’ve booked your flight, packed your bags, and checked in online. You’re ready to go, right? Well, not so fast. There’s one more thing you need to get on the plane: your boarding pass. But what does ...

To use a barcode pass, double-tap your Apple Watch's side button, scroll to your pass, and then show the barcode for scanning. Or, you can open the Wallet app on your watch, select the pass, and ...

But your boarding pass contains a lot more than just your plane seat and gate number. It also includes codes that communicate details about passengers and their itineraries to airport staff.

If you do find this quartet of letters on your boarding pass, allow 15–45 minutes of extra time to get through security at the airport. This story was updated to add a gallery.

Check your boarding pass: If the letters SSSS are on it, expect to spend extra time at security. Here's what triggers SSSS on a boarding pass.

A passenger displays his boarding pass at John Wayne Orange County Airport in Santa Ana, California, on Sept. 11, 2011.