Southwest Airlines offers a service called TSA PreCheck to streamline and expedite the passenger security screening procedure. Southwest TSA  PreCheck travelers who take part in TSA PreCheck, which costs $78 and involves a background check, can get a Known Traveler Number (KTN). This KTN must be added to your Southwest reservation or Rapid Rewards account in order to ensure that you receive TSA PreCheck benefits. You can use faster security lanes on the day of your trip if your boarding pass contains the "TSA Pre" signal. TSA PreCheck allows you to wear belts, shoes, and lightweight outerwear. Liquids and laptops should go in your carry-on. This service is offered at more than US airports.