Originally Posted by
findark
The scanner does indeed reject boarding passes which are not for the flight which is being boarded. The problem arises from the fact that it has one "reject" beep for its many different kinds of rejects: people who board out of sequence, exit row passengers, BPs which aren't scanned correctly, BPs which are scanned twice, etc. Many GAs simply don't look twice at the warning beep and wave passengers though regardless.
This. Except I would say instead that almost always GAs check the screen and correct the problem - ask about exit row, direct to the correct date, provide a new seat, etc. This noise goes off thousands of times a day all over the world. We hear about the issue the once in a blue moon time something fishy happens and it isn't caught. One explanation for this is that because the person did not speak english, and had a translator with her, the GA thought the beep was related to extra assistance and just never looked at the screen and saw it was the wrong boarding pass. The cabin crew also erred it seems in not looking more closely at the boarding pass when the passenger boarded.
But I agree, the problem is the single noise the scanners make. It doesn't seem like it would be that hard to make the noises unique (or prioritize them somehow) but then again, it isn't hard to train the agents to always always check the reason behind the buzz. It is not completely shocking this happens every once in a while though when multiple factors align.