Not to minimize Meta's push for these things, but there have been devices that do this for quite a while now. You can get tiny cameras hidden in pens, watches, glasses, and all sorts of other items.

It's just that in the past, these were sold by janky companies selling them as spy/hidden cameras, not massive multinational data brokers like Meta.

I would be surprised if those don't already exist, I hear stories in the news all the time about small hidden cameras places they shouldn't be. For a private space like the locker room I'm not sure what option there is besides laws making that illegal (I assume/hope that already is?). Someone dedicated already can get a much more discreet camera.

For public spaces, at least where I am, there really isn't a legal expectation of privacy. I couldn't tell if someone was watching YouTube or filming me with their phone and I probably don't have any recourse anyway.

People already sell services to disable the light.