While I have not made it a habit of keeping up with SETI theories, the beacons verses eavesdropping argument is interesting. It seems unlikely that there are any deliberately established beacons out there, at least within a reasonable distance (say 40 LY).

From an admittedly limited perspective, I wonder why an advanced civilization would establish such beacons anyway except perhaps as some sort of navigation device. Maybe it's just me, but shouting out "HERE I AM" to all comers just doesn't seem prudent.

On the other hand, there has been a lot of thought given to discovery of normal RF broadcasts. However, given the inverse square law over incredibly vast differences, it seems rather challenging to pick up such weak signals against the background noise.

There may also be another factor, that on a window of opportunity to distinguish artificial verses natural signals. With only our own technological history to go by, it's possible that the window of opportunity to pick up such signals may be very small.

The first powerful man-made radio signals were transmitted about 100 years ago. They were at a frequency band that would be hard to pick up against the noise background. Over the next few decades, much more powerful signals at better frequency ranges came into service. Perhaps the most powerful and easily distinguishable signals were some of the powerful radars like the Ballistic Missile Early Warning System (BMEWS) units that came online in the late 1950s/early 1960s. Those were directional radio emissions with distinguishing characteristics like pulse repetition rates at specific frequencies.

As the years have gone on, we've began to shift from so many very powerful transmitters broadcasting analog signals to lower powered transmitters broadcasting digital signals. Those digital signals are a lot harder to distinguish against background noise. We're also using more and more fibre optics and directional satellite signals to cover large geographic areas. It's possible that within 20-30 years, the local broadcasting stations may not be nearly as numerous as they are today. This suggests the possibility that the amount of detectable RF emissions from the Earth might be decreasing in the years to come.

If someone had listened for RF signals from the Earth, they wouldn't have detected anything as recently as 100 years ago. They might not detect much 30 years from now, either, meaning the window of opportunity to detect us would be closed. Imagine if the technical evolution were similar on other worlds. If they were as little as 100 years more advanced than us, we might never hear them. On the other hand, if we give up listening, we could miss those who are perhaps a few decades behind us technologically.

Of course, all of this is speculation based on a dataset on one known technological civilization.