It seems like they're calculating the farthest distances where it would be theoretically possible for aliens with Earth level tech to detect us, for various different ways of detection. I'm curious about a related question: At what distance would we likely have been able to detect 'ourselves' with current technology? Ie. if there was another Earth 100 or 1000 light years away, would we have seen it by now? (Assume they are x years ahead so the signals have had time to propagate).

I think it may be a relatively short distance, which could have implications for resolving the Fermi paradox, but I haven't seen any definitive estimates & I'm curious to learn more.