Smoke Signals (Score 1)

Imagine an isolated island where the natives try to establish the existance of other inhabited islands.

They send smoke signals from all the high mountains and look for like back.

As they pronounce the re-affirmation that they are alone there are transcontinental jets flying over their heads, the EM spectrum is full of transmissions and a couple of satelites are presently scanning the island in a number of frequencies.

This poses an interesting problem. Not only do we have to be listening in the RIGHT area of the sky, using the RIGHT frequencies but also the species we try to listen to will have to be at the RIGHT stage of the development. Will we keep listening in Radio when we go to Lasers? Will we keep listening to Radio AND lasers when we move to Gravity waves? etc.