There is a lot of good advice given in this tread, but there is some not so good advice also. What it comes down to is you have to protect your family, property can be replaced. Posting yourself at the top of the stairs while you wait for the police to show is a good idea in my situation but it may not be in your's. Leaving your family unprotected while you investigate may put them in danger. Clearing a room or house is something you should be properly trained to do. Watching videos and reading magazine articles are no substitute for getting training. However, you must make that decision when and if the time comes. Every situation is going to be different, but having a basic plan is a big help in making that perhaps fatal decision.