Sounds like you know a thing or two which is what I appreciate. I don't know what's used and don't have a budget to perform any meaningful analysis. But I do know that GWEN towers are 30 years old tech that's capable of transmitting signal in 200mhz to whatever ghz range 200 miles afar. Frey effect according to wikipedia is audible in 200 mhz - 3 ghz range. According to James C Lin research - signal doesn't have to be strong (in fact, strong signal can get hazardous to health and used like a weapon like in Venezuela operation). Surely radio folks can match up 30 years old tech. And signal processing capabilities nowadays can get absurdly sophisticated.

What are your thoughts on FMCW radars? "Emotion recognition method using millimetre wave radar based on deep learning" research paper is what I find interesting. There also exists research paper that deals with recognition of drivers behavior (logically meaning - FMCW radars are capable of locking onto moving targets in quite long radius). From what I understood (with my limited understanding of the subject) - such radars are capable of picking up EMG signals. and according to wikipedia - EMG is enough to feed neural networks and decipher so called "silent talk" aka your inner monologue.

Another paper I find important: https://ieeexplore.ieee.org/document/6711930 What are your thoughts on radiomyography?