How might you detect a "life sign"?

It's a common trope in science-fiction: "scanning for life signs". A few taps on the screen, and you get an instant population count, often with the ability to distinguish species, and even personal details about the subjects (e.g. "40 life signs, 12 Klingon, 7 female, one of whom is pregnant").

But what data source, or cross-referenced data sources, might be used to gather such data? What would you scan for, and what would you compare it to?

Ideally, it should be able to meet the following criteria:

• The subjects should be at a significant distance, and/or behind obstacles (i.e. you can't just look and count).
• The system should be able to discern between living things and life-like things (e.g. robots, fires, or holograms).
• The system can disregard microscopic or other widely divergent lifeforms like plants (usually we're scanning for humanoid life, or similar). Although, bonus points if you can scan for anything.

Given these constraints, how might a system detect "life signs" within a given planet or structure?

posted over 9 years ago

Nerrolken‭

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