Technosignatures are observable signs of technology that would indicate the presence of an intelligent civilization — as distinct from biosignatures, which indicate the presence of life without requiring intelligence or technology.
Classical and modern forms
- Narrowband radio signals — the 1959 Cocconi & Morrison paper proposed narrowband radio beacons as ideal technosignatures and launched modern seti
- Laser pulses / optical SETI
- Atmospheric industrial byproducts (e.g., chlorofluorocarbons, NO₂)
- Megastructures (Dyson-sphere-like signatures in IR excess)
- Waste heat from stellar-scale civilizations
- Nighttime artificial light — see nighttime-light-emissions; primary calibration target for terrestrial-technosignature characterization via viirs-dnb on suomi-npp (src-terrestrial-technosignatures-satellites-2026-04)
Detection pipelines
A modern narrowband technosignature search applies filters like:
- RFI masking
- Multi-beam / multi-antenna directionality checks
- Doppler drift-rate matching to the target’s motion
- Zero-drift rejection (eliminates stationary Earth-based sources)
- Occultation checks — does the signal disappear when the planet passes behind the host star
- Temporal evolution and visual inspection
Key programs and surveys
- breakthrough-listen — the most comprehensive ongoing technosignature survey
- VLA + MeerKAT K2-18b search (2023, results 2026) — broad, deep null result on a single hycean target (src-k2-18b-technosignature-null-2026)
- Upcoming: SKA (Square Kilometre Array) and ngVLA (next-generation Very Large Array)
Interpretation of null results
A technosignature null does not rule out life. It is consistent with: an uninhabited planet, pre-technological life, or technological civilizations using non-radio, broadband, low-duty-cycle, or encrypted signals.
An additional factor: stellar-plasma-scattering — stellar wind plasma turbulence and coronal mass ejections near a transmitting planet can broaden ultra-narrow radio signals before they leave the home system, causing them to fall below standard detection thresholds. m-dwarf-stars (the most common star type) are highest-risk. Standard seti pipelines account for interstellar propagation but generally overlook this near-source distortion. See src-plasma-technosignature-scattering-2026.
Target Prioritization
caleb-scharf’s 2026 interplanetary-habitable-zone framework offers a physical-resource basis for predicting where technosignatures should be most detectable: Sol-analog systems with accessible asteroid belts up-weight; active M-dwarf systems where civilizations cannot persist (e.g., trappist-1) down-weight (src-interplanetary-habitable-zone-2026).
Earth as calibration target
Earth’s outgoing technosignatures — most directly its nighttime-light-emissions measured by viirs-dnb — function as a working ground-truth model for what an alien observer might detect from a comparably industrialized exoplanet. See terrestrial-technosignature for the full subclass list (nighttime light, atmospheric industrial gases, waste heat, RF leakage) and christopher-kyba’s 2014–2022 global VIIRS DNB analysis (src-terrestrial-technosignatures-satellites-2026-04). The esa-proposed earth-explorer-13 dedicated night-lights satellite would deepen this calibration.