I did see in the news that scientists where looking for radio signals from the star Gliese 581. While there might be habitable planet around this star. I doubt there is any civilization located there. The reason is not that any planet there might not host life. The reason is what it takes life manage to go up to sentient level. The energy output from an red dwarf star is in my opinion just too small to make it. Some of the red dwarf class are so low in energy output that it would not even melt ice at good distance from it’s star.
I also believe the question about habitable zone around star is more then it’s distance compared to how bright it is. It certainly plays it’s role. I do not doubt that. But if a planet is too close to it’s star. Gravity is too strong for life to survive. if it is too far way, the planet get’s too cold. Too close, the planet also has the risk of facing just one side towards the sun and leaving the other part of the planet in eternal darkness. Something that would make life impossible to develop to any major level.
It is my opinion that best chance of finding life is around stars that are similar or same type as our sun. The universe is big and full of surprises. So I am in no doubt that intelligent life exist where I now consider impossible.