In order to be eligible for TSA PreCheck for all airlines that allow for the service, you must have a 'known traveller number' (KTN). You must be travelling on an airline that accepts TSA PreCheck as well as an airport that accepts TSA PreCheck. At Alternative Airlines, we only show ...
Note that adding your KTN to a ticket does not necessarily guarantee that it will be automatically applied to your next reservation. That said, here's a step-by-step guide to how to add TSA PreCheck to American Airlines, Delta Air Lines, Southwest Airlines and United Airlines: How to add...