The Fermi paradox isn't only talking about detecting alien civilizations via radio emissions and the like. More likely would be the detection of a civilization

The Fermi paradox isn't only talking about detecting alien civilizations via radio emissions and the like. More likely would be the detection of a civilization that is harvesting a respectable portion of their star's energy. Energy is power, and stars absolutely dwarf any other accessible source. Once basic space construction is mastered (which we are very close to), large scale solar collection seems a likely path that many civilizations would take. A Dyson swarm would probably be the first step, which would be detectable from very large distances.