1. Although it’s best to put the pads outside of the right wrist and outside of the left ankle, you can place them more or less anywhere and the signal will still permeate the whole body. It’s just stronger between the pads. Although I haven't tried it, is it possible to put the pads on the palms of the hands? If you set the system to have low frequencies at lower voltages that might reduce the risk of a few issues.
2. I always use my wrists as I have issues with my palms. Never bother me.
3. Inside of the wrists should be okay.
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