That's a great question. I'm not totally sure if this is possible. If it was, I think one-way mirrors would use this technology. For now, it seems like they only work because they only let 50% of the light through + there's a brightness differential between both sides. Perhaps someone more informed about this could chime in.

Yeah, there's no magic material that can violate the second law of thermodynamics, because it's the second law of thermodynamics. One-way mirrors are just partial mirrors with less light on one side than the other.

There's no such thing as a "one way tint".

https://en.wikipedia.org/wiki/One-way_mirror#Principle_of_op...

This is a simple implementation of a one way mirror.

Metamaterials have a chance at at: https://www.nist.gov/news-events/news/2014/07/new-nist-metam...

Then they'd have a signature of reflecting less than surrounding. In the long long run, probably more robust to detect the entropy generated by computation in a physical area (i.e. heat) and not the optics.

Agreed. I expect however that any easily available thermal sensing, especially on smartphones (see FLIR, etc), could be easily defeated with a strong adversary doing good thermal management.

As you say though, extra heat is a physical guarantee, so maybe a smarter technique exists to separate signal from noise in the thermal domain that I don't know of yet.