Should the unit get hot?
The manual that comes with the zapper emphasizes how hot the unit gets when in use. My zapper barely gets a little warm in one spot. I have not been getting any results with it. I wonder if it is defective. I would like to return it for a refund, unless when you test it you find it to be defective, in which case I will take a replacement. Please send instructions for returning the zapper
The page you refer to indicates the 16 volt Ultra version. This Ultra edition did get hot when it was originally designed.
Your Zapper Digital Plus 12v model always ran cool. Indications of heat are by no means a barometer to indicate effective frequency output.
The Zapper Digital are designed to give subtle frequencies over a longer period of time. Some people feel the frequency immediately, some peoples skin sensitivity is different.
The Zapper Digital is tuned to the highest voltage/frequency output without causing skin rash/burn, (so it is pre-set to the highest value).
You will likely feel the frequency output more with the silver buttons facing the wrist area than on the palms. Use the Zapper straps on your wrist. with silver button facing the inside of your wrist.