Janq, this story was more about teens and alcohol than it was about firearms safety, at least IMO. Teens can defeat any lock you put on a firearm in reality. Yes you can put them in a safe; I would bet most teens can find the key you've hidden or can guess your combo from other passwords of yours they probably have.
Next issue: where were mom and dad? I suppose this comes from my homeschooling, fundamentalist mindset, but teens home alone plus alcohol equals the real problem.
In my home, I keep the majority of the firearms that are not on me in a safe. That said, the HD shotgun is on a rack in my bedroom with a full magazine, an empty chamber and the safety on. It's three actions away from firing, and with four kids in the house I am completely comfortable with that. My oldest two go hunting with me and know firearms safety well. Even the youngest two know firearms and help me clean them, and go with us when we shoot. They know what guns are for.
The only "safe" method is to teach your kids all about firearms and de-mystify them. The reason this happened was a kid in the home who thought it was a cool toy and decided to play with it, plain and simple. And IMAO the only safety that is worth anything is the one between your ears.
I know you disagree Janq, but if we wanted to truly be as safe as possible we would get rid of the firearms in our home because of the slim likelihood of this, as well as the cleaning chemicals and the prepackaged food if we are being intellectually honest. We all balance an acceptable level of risk. YMMV.