How do you detect if the player has not got any portals placed?

There's a place in my map where the player can trap themselves if they've not placed portals outside. So I need a way to open an escape hatch if this happens.

Must be possible because it happens in a few places in the game.

There is a func_portal_detector, that you could put around your entire map (or at least, all areas reachable from this specific area), and then you could put another trigger in the room/pit/whatever to check and see if there are no portals detected.

I'd try to avoid this at all costs. It's never very fun getting "stuck" in a chamber and having glados let you out; it really breaks the flow of puzzle solving.

That being said, there are a handful of sp levels that include this mechanic and it works just fine.

Meybe you can reverse the problem: Can you detect that the player has placed all of its portals inside, and can you guarantee that the player must have had placed at least two portals to have access to that room (in order to exclude the "no portals" exception)?

I couldn't get the detection thing working, wasn't sure what outputs to use on the func_portal_detector.

I've got a workaround for now so it's not major problem.

If anyones got a tutorial or example I'd like to see it though.