Dear Frictional (some advice)

[Romulator]

But he can open doors. I hid inside one of the rooms and he opened the door, wandered around, and then left. He doesn't just teleport.

OP was talking about the fact that you could lock (not just close) certain rooms in this particular area and with a bit of effort, trap the monster inside.

THERE ARE DOORS YOU CAN LEGIT LOCK!?!?! I guess I AM the idiot, haha. I never knew! I thought you could just close the door on them, not actually lock them out! My ENTIRE gameplay could have gone COMPLETELY different with that in mind. I'm pissed. xDD

In that particular area:

Spoiler below!

Within the security room (when you needed to fix the elevator by uploading data to the chip) you can unlock and lock certain doors. Therefore, you can trap the proxy here. I'm not too sure if you can trap any others in other places.

Fun fact! I was locking and unlocking some doors to try and make it easier for me to remember where to go in that area. As I was leaving, I was just about to open the security door, then the enemy was right there. I crawled back over to the computer and tried to lock it out, then I locked it in the security office with me ;-;