For that matter, ANY gathering at all can be monitored when a bunch of batteries twinkle in unison with more than 10 folks in one place. I get the message here.
People think they can't live without their phones. I will. You betcha.
Even the Bible prophecizes that the number 666 is that of a man...saying 'Be ye wise and calculate his number, and that number is that of a man". King James version may say it a little differently.
This is scary stuff. Tracking individuals in a group could get someone blamed for being somewhere they were not, doing something they were not, and put them in the pot for being replaced for someone who DID do something wrong. It's all gonna work for the criminals in office, and I am NOT saying the ones in office are ALL criminals, but the ones who know who they are.
The omniscient will have the last word. =)