Fusby, I believe that the magnetic trigger locking device you describe was briefly tested by some P.D. somewhere.
From what I can remember, many of the cops involved in the evaluation had a lot of trouble with the magnetic ring. Some didn't feel comfortable wearing it. Others forgot to put it on when they went on duty. Problems with gloves were encountered, and someone pointed out that a kid with a refrigerator magnet could probably unlock the mechanism.
It amazes me that our government will gladly invest tax dollars to develop a "smart" gun, but won't spend a dime on programs that will produce a smart gun owner.