I don't know why your son didn't call, sounds like he isn't trained to standard as you suggest.
Lets take a look at rule number 2 of weapon safety; never point a firearm at anything you are not willing to destroy. You heard and saw something, and decided to skip PID and place your sights on an unidentified target, you were not willing to destroy. You can tell yourself you did the right thing all day, I disagree. There are multiple cases right now where people didn't get PID and waxed someone they assumed was a threat before really making sure, like Renisha McBride. What would have happened if your son had his head phones in and didn't hear your challenge? But hey, this is the internet and my opinion really doesn't matter, you do you.
It sounds like you do have training, and do understand PID, chances seem pretty good that even if your son didn't respond with the correct password to your challenge, he would have lived. Sadly there are numerous stories where it is the latter.
And just to correct something, you use a challenge and password, not a running password. A running password is when you are approaching friendly lines under duress or being actively engaged, and don't have time to conduct a proper link up or passage of friendly lines. If you had a running password, your son would have been screaming the password as he was approaching your house until he was inside and on the other side of friendly lines.
Anyways, cheers on trying to keep your family safe and doing what you think is best for them.