Didn't Israeli students show that you can recover audio from the vibrations of bulb filament with a fast photo diode?

I'd test that with a CCD line sensor plus a wide aperture lens and reading it out with 8kHz. Then you have 128 audio pixels that can cover an entire city.

Line of sight might be an issue there. I'm thinking more high-end clandestine eavesdropping. Fun fact: curtains are a pretty good defeat for laser microphones, but if the building is really old and made of solid stone, you can point at the rock instead!