Thankyou for sharing your real-world experience of this. You are right about tuning out, laptops are just a more visible sign of that.

I am rather a loud-mouth with great job security, so I will tell pretty much anybody, without cruelty or judgement, that their meeting is not relevant to me. For those less bull-headed or with more precarious employment we need to invent a pocket “clicker” that would indicate to the meetings chair/current presenter that he was losing attention.

Birmingham University in the UK used to have something called a “lecture cube” for gauging the speed or uptake of a lecture. Perhaps that could be adapted to big meetings?