If you don't know what it is, it is a computer in communications telling you which way someone went. Here's some pics:
So the way it works is in a hallway with glass floor with three ways leading southwest, southeast, and north.
If you pass a line that is the the end of the hallway, it will light up (it's a cool detail I found) and then the door log will tell which way you go.
Here's another pic:
So the goal to counter this is to kill the person who is on doorlog….. nah just kidding, the goal is to not pass the sensor line and use the vent.
So let's say someone pass the north sensor, don't pass it, instead use a vent to go up a room up there and find the person then get a perfect time to kill (As in: getting your kill ready, make sure the target is close to the vent then kill) And it the log, it shouldn't said you pass and left the north sensor.
I really hope you guys see this and use it, maybe if two people are in different rooms, maybe kill one then hope the other one goes down then that person gets caught (If someone smart enough is using the doorlog)