Safe Zone Combat System

Lately I've been seeing several "safe zone combat systems." These seem to involve some kind of sensor that a participant wears, and a scripted weapon. I know I've seen swords in use, and I believe other edged weapons. The sensor tallys cumulative weapon effect and announces when someone has "died."

Any speculation as to how such things might work? How does a sensor know it's not affected by a weapon wielded by the same person wearing the sensor? When person A swings, how does person A's sensor ignore it, and how does person B's sensor (and not person C-Z, also present) decide person B was hit?

The sensor is used by the attacking weapon, it scans for targets and then reports via llSay or some other method to the target that it was hit. If you're wearing the sensor, it won't sense your avatar in the sensor event so you don't have to worry about hitting yourself, which is the big plus to using this.

Edit: Actually, using sensors isnt limited to only safe zone combat, it could easily be used in things that do damage. The reverse is true also, you could use bullet type damage in a safe zone system.