Other than a crashing noise, if it is just an alarm or even a muffled sound, how about a very bright flashlight or a hall light on?
Without a loud sound, how do you determine that it is not a family member?
If a stranger is clearly identified, the Mini 30 will work.
How many people would simply make an assumption and shoot into a dark hallway or room?
A guy just killed his fiance recently due to an assumption, and he's not the first to have killed a family member etc.