What might extraterrestrial civilisations do to send electromagnetic signals into the space? It could be for entertainment or navigation, or to ping our solar system and see if there is anyone home. It doesn't matter what they are doing, but detecting these transmissions is the best way to prove to humans that there is someone else out there. Astronomers have been trying to listen in on alien broadcasts intermittently for the past six decades.
SETI is the collective name for these initiatives. The history of SETI dates back to 1960 when Frank Drake pointed an 85-foot long antenna at two star systems that were relatively close to each other in the hope of picking up an alien message. The experiment lasted two weeks and used equipment that was already available. Drake's work was not successful in detecting any transmissions. However, it excited the public. This led to further attempts.