If you are armed, you should tell you family and friends to always call before showing up unexpectedly, especially when you are not at home.
Your advice is sage but I have some questions:
First, the guy was a cop, his son would already know his dad would be armed.
Second, how would the son show up randomly if not already aware that's where dad was staying?
Third, dad would have had to give the son access to the room for him to enter??
Too many detail missing here.