[AnthonyMouse]

The technology exists but the false positive rate is high, most cameras don't actually implement these things and there is no convincing evidence that all cellphone cameras are secretly always on (though a compromised device could be).

[TeMPOraL]

I tend to think of it this way: it's theoretically within our technological capabilities, and has been for at least a decade. However, it's fractally difficult - there are technical challenges, political issues, PR issues, principal-agent problems, all mixing together - and importantly, there is no strong enough economical (or political) incentive to do it. Not when doing a small fraction of work, and a shitty job at this, still showers you with money while avoiding most of the problems.

An not to push my favorite TV show that doesn't involve aliens from outer space too much, but recent advances in AI are changing the equation here, making Person of Interest even more accurate and relevant than it already was.