I would guess advanced civs don't bother with radio and look instead for direct visual and spectrographic evidence. We're very close to being able to look for

I would guess advanced civs don't bother with radio and look instead for direct visual and spectrographic evidence. We're very close to being able to look for spectrographic evidence and maybe 50-100 years from building a telescope that uses a planet's gravity well for optical enlargement. Earth already looks quite distinctive spectrographically because of the free oxygen, water, and CO2. In the general case you look for chemistry that is far from equilibrium. Hubble already has the sensitivity to analyse exoplanet spectra, and Webb can do much better. But some way beyond that, I'd imagine it's possible to look for spectral technosignatures directly. Artificial lighting, heat sources, and unusual non-biosignature gas combinations would all be clues that life exists. I'm also fascinated by Przybylski's Star, which must be one of the weirdest objects in the galaxy. It doesn't take much imagination to wonder if it's an artificial beacon. https://en.wikipedia.org/wiki/Przybylski%27s_Star https://en.wikipedia.org/wiki/Przybylski%27s_Star