Seeing and Hearing The AI, including your own Squad, acts in response to sounds and site. They can hear from further away then they can see. When a noise is made, they'll start to investigate, but if they do not see or hear anything additional to the previous noise, in time, they will return to their normal status. The AI can only see in a 90-degree field. If the AI is wounded, sometimes they may run for a safer area.
Visibility is affected by posture.
When standing you are the most visible. When prone you're the least visible. This also is affected by how much you're illuminated. You are less visible if you are in the shadows. Using your flashlight makes you more visible.