In our hypothetical dystopian future The Regime will probably jam 2Ghz to 5Ghz in public spaces. TEMPEST mode would also force them to install vibrators into all coffee shop tables.
You are misusing the term. TEMPEST is an attack.
> Perhaps vibrate mode on one phone being picked up by the accelerometer of another?
At very close distance vibrating our vocal cords and eardrums would be much easier and works without battery.
In my dystopian future theory, the government that has no issue jamming 2 and 5 ghz channels to keep people from talking would probably notice two people on on a table continually picking up And dropping their phones. Why wouldn’t they simply whisper to each other in that scenario?
The classic example is pointing a high speed camera at an office window across the street and recording the brightness of the walls. Even if the office computer is hidden out of sight the attacker can reconstruct what’s on screen by analysing subtle changes in brightness reflected off the wall.
Is this feasible now?
Old BBC documentary on the topic