I have a feeling this is going to involve NIR-II with fluorescent particles. To be clear, I'm not advocating for this, the thought of it freaks me out. Just because something isn't physically invasive, doesn't mean it isn't invasive in other ways!
Me thinks it's the thought that it could work that is freaky, not the mechanism itself. If you think governments demanding backdoors to encryption is bad now, what if that tech worked? All it would take is a kidnapping case like in "The Cell" for things to get very uncomfortable.
