TSA PreCheck is a service provided by Southwest Airlines that expedites security checks at some airports. Southwest TSA PreCheck holders are permitted to remove their light coats, belts, and shoes, and carry-on baggage only include computers and compliance liquids. You need to apply for TSA PreCheck, have your background checked, and have a Known Traveler Number (KTN) in order to use this service. When you book a ticket with Southwest, enter your KTN, and your boarding pass will show your TSA PreCheck status. This makes using dedicated security lanes possible, which expedites and improves your airport experience.