Known Traveler Number: What is it, and why should you have one?

Whenever you book travel, there are probably a few key pieces of information — like a flight confirmation number, passport details and airline login credentials — that you like to keep handy.But if you're a member of TSA PreCheck or Global Entry, there's another key piece of information you should always have at the ready: your Known Traveler Number.That nine-digit code is your ticket to the TSA PreCheck lanes. And it's often the thing that's missing if you ever check in for a flight and find your boarding pass doesn't have the "TSA PreCheck" mark.Here's what to know about getting a KTN, how to find it and how to make sure it's attached to your flight reservations.What is a Known Traveler Number?A Known Traveler Number, or KTN, is a special code that's assigned to every TSA PreCheck and Global Entry member.It's often a jumble of numbers and letters, sort of like a frequent flyer number or confirmation number.But it's not assigned by an airline. Rather, it's from the U.S. Department of Homeland Security.It proves you're an approved, vetted member of TSA PreCheck, Global Entry or one of the other federal Trusted Traveler Programs, such as Nexus or SENTRI.And it shows the TSA that you...