<...One might argue that we are not yet capable of detecting it either, if the technology used to transmit is so much more advanced. It may be like trying to examine a microchip with a magnifying glass.... like assuming the message will be in braille, when it is actually a DVD. In these examples not only is the message more densely packed, but it requires fundamentally different technology.

This statement makes an important point. A vast majority of our current methods of moving information: radio, television, DVD, fiber optics, etc. would have been a complete mystery to even brilliant people as recently as a hundred years ago. During the childhoods of people alive today, these technologies would have been as far beyond them as the technology of the Krell in "Forbidden Planet." And this is only a hundred years!! Hell, half the stuff I use routinely still smacks of sorcery to me. As I stand on the corner of my street, I see and hear nothing, yet gigabytes of information--pictures, words, data--wash through me as radio and TV waves, from towers, satellites, cell phones, and other sources; and pour through the buried fiber optic conduits beneath my feet as light beams.

If there are alien species a thousand years ahead of us--a geological eyeblink--their technology would very likely be completely over our horizons.

Listening for radio signals from space may be as quaint as some lost tribe in Africa assuming that more advanced civilizations would use really, really big drums to communicate. Still, the attempt is worthwhile. Who knows?

So how DO we detect a planetary civilization in another solar system? Is there anything that civilization emits, regardless of the level of technology? Well, the laws of thermodynamics would suggest that at the very least an advanced civilization would emit heat, and maybe light. Much of our planet looks like a Christmas tree at night, and our cities glow brightly in infrared. The bad news: such light and infrared emissions are nowhere near powerful enough to detect at great distances, even if they were not washed out by the radiations of their star. One would have to send interstellar probes to search at closer ranges. Not easy.

A Dyson sphere would emit infrared at astronomical levels, but how would that be distinguished from some dim brown dwarf star?

The only hope may be if a civilization deliberately attempts to communicate using more primitive technology. If we were trying to talk to that imaginary lost African tribe, we would be idiots to beam radio signals at them. We might get some drums.

All of this is based on so little real data, that speculation is almost useless, even if it is fun.