Great idea, always tried 'watch direction' in case this was already a thing. I agree with a few of the nay-sayers in that this could be potentially OP with everyone just looking out the door.
A potential solution would be that your TP gets changed to "Steve is watching out the north door" and that character receives says/poses/actions at a vastly reduced rate of accuracy (likely based on perception/agility), maybe to the point where all says are reduced to the equivalent of a whisper and whispers aren't noticed at all. Probably put the character at a disadvantage for combat too.
Basically, if you're invested in the next room, you should suffer in the room you're in, but that shouldn't mean that you can't stand by the door and keep a look-out.