Surprise, ready, and actions out of combat.

[Powerfamiliar]

There is a thread in the paizo forums about readying actions outside of combat and it made me ponder the following scenario. How do you guys believe this situation is handled by the rules and how should it be handled by the DM?

The PCs are fighting their way through a castle. A slightly paranoid guard wholes up in a room, grabs a crossbow and decides he is going to shoot the next person to enter the room. The PCs are approaching, but he does not hear them, they don't hear him either. A PC enters the room. What happens? It seems by the rules you just roll initiative making it very unlikely that someone gets to move up an attack the guard before he gets a chance to react.

What if he would rather not get in a fight at all though so he yells: "Anyone that steps through that door is getting shot!" over and over. He still fails to notice the party, but the party is obviously aware of him. Does the party now get a surprise round on the guard before he gets to react with his warning?

[S_Grey]

I'd still just call for an initiative roll. Opening the door wold essentially be the player's surprise round should the guard be unaware of them.

There are plenty of precautions the players could take to avoid being shot, even without knowing exactly what is going to happen.

[Person_Man]

Ready is an action you take in combat. "Readying" an action prior to combat is covered by the Surprise Round, which only occurs if creature A is aware of creature B, but creature B is not aware of creature A.

So if the guard doesn't hear the players, and none of the players don't hear the guard (and shame on them for not Listening at every door and Taking 10 or 20), then I would just roll Initiative, and maybe give the guard a circumstance bonus.