Going into full paranoid mode, I wonder if some other sensors / components can be used as a makeshift microphone. For instance, a sufficiently accurate accelerometer can pick up vibrations, right? Maybe even the laser in a CD drive? Anything else?

Camera + bag of chips: https://people.csail.mit.edu/mrub/VisualMic/

A condenser microphone is just a capacitor. Your computer is full of them.

They are very low level input and generally need a pre-amp just to get the signal outside the microphone. However conceptually at least they are there and so maybe someone can get it to work.