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there may be some issues with the range of harmonics produced.
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Your opinion about what a zapper should do to be able to damage/kill harmful organisms. There is still no proof about what produces the killing. It could be the square wave signal alone, the intensity of the wave, the frequency, the impact of the electrisation on the molecules in the body, the impact of the signal on the behavior of the harmful organisms or on the immune system cells.
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Also, it should be battery operated.
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Your opinion and your positionning to sell your devices.
A device can be safe if properly designed with one or more fuses with a maximum allowed intensity, you can add a 30ma fuse easily between the output electrode and the skin electrode.