SETI
So far SETI has failed to find anything. The only radio civilisation we know of is our own, perhaps we are unusually quiet still we are the only currently available sample so it might be worth considering at what distance we could detect a civilisation like our own.
From http://www.jb.man.ac.uk/research/seti/questions.html
Can you give some idea, in layman's terms, what kind of signals you could possibly detect, for example, how close would ET civilisations have to be in order for us to detect signals like TV transmissions?
Jill Tarter:
Too close. We don't put much power into our TV or radio transmissions because their intended audience is not very far away. Our defense radars are much stronger and the current Phoenix search could detect that kind of signal out to the limit of our current search which is 155 light years. The strongest signal generated by our technology is the planetary radar on the Arecibo radio telescope and we could detect its signal half way to the center of the galaxy. The types of signals we look for are those that have their power concentrated into a very narrow band of frequencies - more compressed in frequency than anything that nature is capable of doing. We take this monochromatic (single frequency) signature as being evidence of technology.
So for the strongest fairly constant signals we emit would be visible at about 155 light years, with highly sporadic signals visible up to about 13,000 light years. So realistically we could only see a civilisation like our own if it was pretty close. It is possible that the Wow! signal was one of these sporadic signals that the Big Ear telescope just happened to see.