Back in the 1960s and 1970s, revolvers could have a “personal” safety installed that consisted of an internal magnetic connection to the sear. The owner/shooter would wear a steel ring to make it work. No visible alteration could be seen, and without the ring, it wouldn’t shoot.
That fails immediately when your "strong hand" gets injured and you must shoot with the other one. The one without the steel ring. No dice. It has to work with either hand with no extra crap and even if the hand is injured, dirty, bloody or otherwise impaired. That happens in a fight for your life.
“Mag-Na-Gard.”