Whatever it is, it would have to be way out there for us not to see it or capture the communication. Their technology would probably appear God like to us.
Indeed. Just imagine how our current technology would look to someone living just a hundred years ago in 1919.
Some new inventions from 1910 -1919:
The zipper
The Oreo Cookie
Stainless Steel
First Crossword puzzle
First Pop-up Toaster
Lifesavers candy
First Military Tank
At our current accelerating rate of advancement, just think where we'll be a hundred years from today in 2119. I'm pretty sure the vast majority of us can't imagine that future.
If they used quantum entanglement transmission technology we would never detect them.
If such a technology could be made it would be totally hacker proof, you could never listen in.
Only the two individuals sending and receiving could be in the conversation.