It all comes down to if the safety of you or your family is at stake. The 90yo women with a shotgun in the room is definetely justified. If you read the code section (its really not that long) it covers that. Deadly Force is more justifiable for your Home Invasion scenario vs. the cat burglar sneaking around. The way I look at it is that I would say that deadly force is certainly justifiable if you have someone in your home and he has a screwdriver or crowbar (he had to get in the house somehow and most home invaders arent very adept at lock picking). With that in mind, he is definetely armed and constitutes a threat. Order him to freeze and get on the floor if he does anything other than get on the floor or run away, I think its justifiable. Just remember shooting somebody in the back if they try to flee is a definete no-no and most likely will get you a date with the District Attorney and a Superior Court Judge.