If you choose to do so, you'll only be eligible to go through TSA PreCheck when you're flying on that FFP's airline. 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 ...
You can add TSA PreCheck to your ticket by adding your TSA PreCheck number to your airline loyalty program's profile or your existing airline reservation.