Don't get me wrong, I agree 110% that you want the element of surprise on your side and not theirs. OK, maybe I did read too much into the original post, but it just seemed that that was more emphasis being placed on what happens after the guys break in and not so much on keeping them out in the first place.
As far as not knowing you have a firearm until that critical moment, I believe there are basically 2 things that an intruder does not want to hear:
1) Dogs barking - we have 5
2) A shotgun being pumped - I want the intruder to be damed well aware that I am armed!