Why do enemies randomly turn hostile?

When I silently kill an enemy with my melee weapon, sometimes an enemy quite far away randomly seems to turn hostile and alerts everyone in the room. In a room with about 8 or 9 enemies, this usually means each player taking heavy damage, and heavy ammo expenditure.

Why does this happen? And how can I avoid this?

Solution 1:

I've been wondering the same thing, and there actually is some mechanics involved. I've done some research and testing, and found that this video is a pretty good one to watch to understand their mechanics. Here is what I've learned:

• When a sleeper is glowing white, it's performing a "scan". If you are close enough, if you make noise either by moving, crouching, standing up, killing another sleeper, etc., it will progress to its next alert stage (the pulsing heartbeat-like stage). Here's a picture of one glowing white:

• You can force a sleeper to perform a scan by making noise, or shining your flashlight on it quickly. Killing a sleeper while another one is nearby will cause it to start scanning.
• If a sleeper starts pulsing, hold still. You can look around, but definitely do not move at all or make any other kinds of noises! If you do move or make a sound, it will become fully alert (glow red), and the chaos will ensue.

It can be difficult to dispatch groups of sleepers silently since the sleepers tend to scan all at different times, making it challenging to pick them off one by one. You have to either time your kills between the scans, or you can force the sleepers to change their scan cycles by making sounds or shining your flashlight on them quickly. By doing this, you can make timing things easier on yourself.

Two more tips - the video pointed out that when your cross hair shrinks in size, it means you are within melee distance of a sleeper. This is good to know when you are trying to charge up your melee attack to hit them. Second, swinging your melee weapon does not count as making noise, so even if a sleeper is scanning, you can swing your melee weapon without causing a disturbance.