They appear to have patented a method that's based on infrared emitters installed in the venue. See page 7: http://pdfpiw.uspto.gov/.piw?PageNum=0&docid=09380225 - that seems to be only the drawings, not the full filing, but it's patent #9380225 if you want the full detail.

I'm not surprised that they have not implemented this. It would take about five minutes for someone to reverse-engineer one of the beamers, and then about five more for someone else to turn it into something you could hang off your keyring to mess with people, and about thirty seconds after that to produce a huge consumer backlash.

Yep, but would you ever buy a device with such a feature, even though you hate compulsive smartographers at concerts?

I sure hope not. That sounds sketchy.