How to make Combine Only doors?

Hey there,
I’m trying to find out how to make those Combine-Only doors as you can find in most roleplaying maps. (rp_c18_v1 for example)
But I still didn’t figure out how they did that… Would anyone be so nice to explain that to me?

-K33rFY

Well, i guess this is exactly the thing you need:

http://www.interlopers.net/tutorials/6551

Theres a simpler way, just make it so “Use Opens” and “Touch Opens” in the Flags is unchecked

Maybe player clip too?