Actually, the reason we will never detect signs of technologically sophisticated alien life is because (i) such civilizations are almost certainly extremely rare, (ii) any that do exist are likely to be so far away that detection will be infeasible even with our best instruments, and (iii) the chances of any two technologically sophisticated civilizations existing in the same period of time and close enough for detection are zero. Amusing sci-fi entertainments have created an entirely erroneous impression, and silly intellectual errors like the Drake Equation have compounded the problem. But when we pause to consider the matter more carefully, it becomes clear that to all intents and purposes we are entirely alone and always will be, right up to the moment where we accidentally exterminate ourselves due to our inability to cope with the amazing technologies created by a few clever people and then placed into the hands of morons.