How do I activate a horde when a door opens?

So, I need a horde to come and attack when a door is open’d. How?

A L4D zombie horde?

Are you trying to make it a panic event?

Yeah, yeah, I am.

I don’t have l4d, but assuming alienswarm is kind of the same.

I believe Firegod got it spot-on.


You can always go here for more detail: