7. What Have We Found So Far?

No extraterrestrial technosignature has yet been confirmed.

This does not demonstrate that technological civilizations do not exist. The search has examined only a small fraction of the possible stars, frequencies, signal types, power levels and observation times. It is often compared to sampling a small amount of water from an ocean and concluding that it contains no fish.

Environmental searches and radio SETI are complementary:

• Radio SETI may find a powerful or deliberate transmission.

• Atmospheric studies may find long-lived industrial chemicals.

• Infrared observations may reveal large-scale energy use.

• Optical observations may detect artificial light or engineered structures.

The best strategy is therefore to search in many different ways and compare independent evidence.