From 1960 until 1998, the scientific search for extraterrestrial intelligence relied primarily on a single strategy: (1) using radio telescopes to find an artificial signal from many light-years away. In 1998, the field expanded its array of search strategies from one primary strategy to three by adding optical SETI and solar system SETI. Each of these three current major strategies has a good chance of success. (2) Optical SETI uses optical telescopes to find a pulsed laser message or some other artificial signal from many light-years away. This approach has several advantages. It is covered thoroughly at Stuart Kingsley's www.coseti.org website and was discussed extensively at this conference. (3) The third current strategy is solar system SETI. This is an effort to detect irrefutable scientific evidence of any highly advanced intelligence that has reached out planet or somewhere else in the solar system. Extraterrestrial civilizations and their technology are likely thousands of years older and more advanced than ours. Consequently, they could send a small super-smart autonomous robot probe to explore our planet and monitor our telecommunications. To make contact with such a probe, about 80 SETI scientists and others have placed an invitation to ETI on the World Wide Web.
Allen Tough, Allen Tough,
"Widening the range of search strategies", Proc. SPIE 4273, The Search for Extraterrestrial Intelligence (SETI) in the Optical Spectrum III, (3 August 2001); doi: 10.1117/12.435362; https://doi.org/10.1117/12.435362