Berserker Hypothesis
en.wikipedia.org
en.wikipedia.org
And if they are at our current level of technology they would be stuck on their planet like we are and have no viable way to reach us no more than we could reach them.
Or they could still be using radio but using fully encrypted communications. Weak signals reaching Earth from over vast distances would appear like and get lost in the background noise of cosmic radiation.
Even encrypted communications MUST be different from space/star emissions.
What Quantum communications are, they will very early show you, that somebody hearing your quantum emissions.
And yes, if aliens will hear our cellular network, they first will see, that Earth radio emissions are just about Sun radio emissions, they will not understand content, but will see too much radio emissions from planet.
If we will use Quantum radars (lasers) to probe nearest stars, we will know very fast (speed of light), that somebody intercept emissions.
So, exists possibility, aliens already know that we looking on them (hear them), but they remain undetected, and same trick could use Earth.
Sure, aliens could use data from such probes, to make shadow shields, to not emit to sides, where detected hearing.
True but at the same time we would have to be looking for it but we're currently mostly concentrating on radio signals.
Just radio emission is not enough to prove something artificial. For example, Jupiter have very powerful radio emissions, you could receive them by ordinary radio receiver.
But radio emissions are most comfortable to work with, that's why PRIVATE persons invest to this.
So, most probably, these effects will be widely used to detect hearing, but communications themselves will be some sort of classic encrypted, for better speed.
What is the most prevalent/enduring symbiotic relationship?