I really like Issac Arthur's treatment of this topic: https://www.youtube.com/watch?v=k7fLNvpl0c8 https://www.youtube.com/watch?v=k7fLNvpl0c8 The easiest tech

I really like Issac Arthur's treatment of this topic: https://www.youtube.com/watch?v=k7fLNvpl0c8 https://www.youtube.com/watch?v=k7fLNvpl0c8 The easiest technological species to detect for the longest time would be space-faring species that leave behind structures on airless moons. Note that even these traces aren't eternal. Micro-meteoroids and meteoroids will eventually erode even those.