Jupiter enemies become alert at random

[OvisCaedo]

I've gone prowling around on jupiter a few times, and noticed that the enemies have this strange ability to become fully alert (full red arrow) while walking through the room invisibly and not making noise. it does not happen with consistency, as earlier I walked through a room and had only the vapos crewman furthest from me suddenly become fully alert while the closer ones continued to stand around as if nothing was wrong.

Edited June 5, 2019 by OvisCaedo