Assume for a second there are alien technological civilizations and they're so bored that they watch us. Low probability but not quite zero.
How do you find them? Large radio telescope arrays? Nope - dustpan and brush... Find somewhere they'd be sure to be interested in, sweep the place and have a damned good look at the debris you find... If they're using nano-technology some of the dust will be, ah, 'interesting'... (Why assume nano? Because if it's larger we'd see it, and smaller probably wouldn't resolve wavelengths they'd be interested in. I suspect it'd be hard enough to pick up sounds with anything too small to see with the naked eye, let alone nanoscale, for example).
But there'd be a lot of dust to look at and a lot of false positives to eliminate, so ideally you'd want to know roughly where to look in order to concentrate the effort, so then I wondered if a world conspiracy of intelligent and enlightened governments couldn't get together to create an international event of such magnitude that any thinking creature would be unable to resist monitoring it - and voila - as if by magic we arrive at the only plausible explanation for the Eurovision song contest.
(I had the basic idea a while back as the first part of a spoof SF story where we start out looking for alien monitoring and wind up inventing very bad tempered and belligerent artificial intelligence as a result of the code that was written to perform the data analysis on the garbage collected getting smarter... Don't worry about it. It was going to be one of set of paradoxical solutions to the Fermi paradox, but I'll never get round to writing any of them... My favourite was health and safety (H&S) - and if you don't understand the connection between H&S organisations and the reason why there are no advanced civilizations out there count yourself lucky. While you're still allowed to do anything as dangerous as counting, that is...
I've been pondering some ideas for spoof stories about H&S bods coping with a multispecies future society, shades of James White's Sector General stuff... But they're something else the world will have to struggle to get along without, I suspect.)
 Spot where the surrealism takes over.