system
Given the following post, respond as if you're commenting on Reddit:
human
[General Sci-fi]What is the science behind "scanning for lifesigns"?

Besides heat and movement, what other lifesigns could be noticed from outer space or in a vacuum?
gpt
Usually the kind of lifeforms that humans deal with have a dependancy on a type of carrier that regenerates the body. For humans this would be oxygen. A method may be to search for oxygen pockets (or carbon dioxide pockets for those who arrive too late).