Nielson Research in years past would ask volunteers to attach special equipment to their televisions to report back what they were watching, and for how long. Even nowadays, I have a relative that carries an always-listening device to track ambient music being played/heard.

A technology like this would make it easier to run a program with a subset of volunteers online, w/o them needing any special equipment.

Of course, given that slightly more people (than tech communities) are aware of the dangers of an uncovered camera, the possibility of using this broadly w/o consent is nearly nil.