As far as I know it has to do with the circuitry. Simple electronics flashlights ok, led flashlight nogo. Late 60a-early 70s autos ok, problem with computers in late mod. cars among other sensors and crap. Put any electronics you don't want fried in a metal ammo can or any sealed metal container. Only problem is I don't know how to tell when It's over and safe to use items. Is say a pacemaker would be knocked out. I'll look into it a little more and let you know more tomorrow.