On Friday, I went to meet a guest arriving at DEN. Since I had about 20 minutes before their flight, I walked around the 2 checkpoints in the main hall. It wasn't very busy at the time I was there. Anyways, at the entrance of both main checkpoints there is a TSA worker with an iPad looking device. As a passenger approaches, the worker intructs them to touch the screen. The screen then shows an arrow. Get a left arrow and you are directed to the regular screening line or get a right arrow and you join the TSA Pre-check line. If a family approached the line, only one person had to touch the screen. The arrow selection seemed to be fairly random but I didn't count the arrows vs passengers.