It depends how you "find" something. If you're using active radar, you can pick up any object of sufficient size, but you can't tell a rock from a person from a ship except for their size. This will not help you at all if the person is floating amongst asteroids, for example.
If you're using IR, you can pick up a warm body and distinguish it from say, a piece of shipwreck. If you're using EM, you can only identify things like bodies at extremely close range.
BTW, the page on the Red does not say it can find people floating in space. All it says is it has long range scanners, so don't overthink it. It is much better to understand how the three basic functions of scan will work and go from there. This is necessary, even for basic things like understanding how missile locks and their countermeasures work.