The Arecibo message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo radio telescope in Puerto Rico on 16 November 1974.
The Wow! signal is the name given to a strong narrowband radio signal detected by Jerry R. Ehman on August 15, 1977, while he was working on a SETI project at the Big Ear radio telescope of The Ohio State University.
The search for extraterrestrial intelligence (SETI) is a collective term for the scientific search for intelligent extraterrestrial life. For example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other worlds.