there's no expectation that anyone will be undressing in front of it
IANAL, particularly not an Irish lawyer, but in the US I believe a court would very likely find a reasonable expectation of privacy regardless of what room the camera was in. In fact, it's well-established in US jurisprudence that the reasonable expectation of privacy includes not only the interior of the home but its curtilage as well, except for areas in plain view from public property.
In principle, in the US, I suspect that if:
- a home had a back yard surrounded by a privacy fence, and
- the homeowner installed a surveillance camera with a view of the back yard, which was not immediately obvious to people in the back yard, and
- the homeowner listed the property on Airbnb
then licensees would have a plausible case for suing for invasion of privacy even for activities conducted in the back yard, and the "child pornography" argument would be viable. That is, the REoP would apply to the licensees even outside the house, in that portion of the property, because it's curtilage not in plain sight from public property.
SCOTUS has been pretty clear about how REoP attaches to curtilage, as recently as last year. Of course, with today's SCOTUS, we'd probably have Gorsuch Kahn arguing that everyone involved should be summarily executed, just on principle.