Just thinking off-hand and simplistically, pulsed acoustic waves (i. e. sonar) can penetrate and pass through substances insulated from optical (visible, infrared, gamma rays) or electromagnetic (radio, microwave) spectral access.
The acoustic waves of rather pure pulses could be modulated by sound waves within the environment in the path, with the resultant emerging waves being recorded and deconstructed by differential Fourier analysis to obtain the sound patterns (speech, tones, etc.) separated from the injected sonar-type waves. Both reflected and transmitted pulses can be analyzed for speech and movement, if this guess is a possibility.
The only defense would seem to be a totally comprehensive insulation from injected acoustic signal by completely absorbing it ere it reaches the ambassadorial offices, or by detecting acoustic emitters/sensors incorporated into the physical design of the building and/or each room.
It is this last phase that would be suspect.
It is one thing to sweep the room for transducers that convert acoustic waves to electronic signal, but quite another to discern the presence of detectors that are coupled with visible (fiber optics) or acoustic methods. IMHO. Actually and obviously, the human cephalic structure can be damaged severely by acoustic shock, citing the sports of boxing and football, the combat exposure to explosive events (used to call it shell-shock), or employment noises like riveting, jack-hammers, sirens, constant humming of large magnetic inductors or transformers (NMRI which most certainly tracks physical activity of the brain, or large power-plant voltage transformer/inverters).
Gives the layman some food for thought as well as requests for explanation of this kind of experimentation and snooping.
In my VA volunteer service experience I became acquainted with a seriously brain-function-disabled veteran who as a radar engineer got his head in the way of a high-power microwave beam, and almost completely lost his control of motor skills, although he could communicate laboriously that there was nothing really wrong with his critical thinking faculty. And I myself, having undergone the shock of having my cranium opened for a meningiotomy and resealed, temporarily lost the control of transmitting thoughts by speech (but not through writing). Eventually I pretty much recovered from it, but I don't know now whether my more frequent memory lapses come from aging only, or if there is a residual loss of mental agility aggravated by the surgery- and/or meningioma seizure-induced damage. Stress and/or sleeplessness can make that effect temporarily worse.
We ought to be diven more, much more information as to what is affecting our diplomats, as well as how and why.
diven given
>> We ought to be given more, much more information as to what is affecting our diplomats <<
Not sure I can agree.
We may not want to let the perpetrators (i.e., the Russkis and/or Chicoms) know the extent to which we have scoped out the technology in question.
Also, we may not want to divulge info that might help OTHER nations develop similar stuff.