IIRC, the amount of radio waves leaking from Earth into space has decreased substantially over the last few decades. I wouldn't be surprised if energy efficiency gets to the point where, if a foreign alien civilization notices radio waves from Earth, by the time they transmit a round-trip back at Earth we'll have long since stopped leaking terrestrial radio waves by accident into space.
True, but our radio telescopes have also been improving. The Square Kilometre Array, under construction in Australia, would supposedly be able to detect "an airport radar system on a planet 50 light years away". I suspect that an advanced civilization 500 ly away would still likely leak enough radio for us to detect it with current or near-future technology.
Unless their technology developed along a completely different path, and the concept of radio waves is too foreign to them because they use an altogether different method of communication that we can't even begin to imagine.
