A zapper does not put out a electro magnetic field. it puts out a positive offset square wave voltage. Pretty close to pulsed DC.
I have a magnetic pulser that puts out 50,000 Gauss. It takes a huge capacitor to store up enough electrons to put out the instantaneous Amps necessary through a coil. And this magnetic pulser is very beneficial in healing and in killing pathogens by inducing micro currents into the pathogens.