Spirit, on which the current incarnation of Frontier is modeled, doesn't offer it either. Nor does the other Ultra Low Cost carrier, Allegiant. These guys use a number of secondary airports like Latrobe, Trenton, Atlantic City, Goodyear (AZ), Niagara Falls, etc. They market discomfort, as a trade off for cheap fares. Having pre check would be inconsistent. It also requires an expensive rewrite of their IT software. I'm going to guess less than 5% of their customer base would ever pay the fee. As an aside, I had occasion to use Spirit at DTW, a few months ago, and TSA were arbitrarily directing customers (including me) to the less crowded pre check lane. When they first started doing that, the airlines were making those selections, presumably based on FF experience. It now seems anyone can be waivered at the checkpoint, based on physical profile. Among other things, it begs the question, why are we one of the only countries in the world that makes people take their shoes off in an airport?