It won't. All it does is make a beeping noise and it's up to the gate agent to send the passenger to the back of the line or allow them to board for XYZ reason. A week or so ago it happened to me. I had a co-worker board with me as I was in Group 1 and he was in Group 9. Just as in the past, I told the gate agent he's with me, he scanned his pass, now the machine beeps, agent clicked a button or two and he was on his way.