A Zapper is a simple electornic device, which according to Dr. Clark, kills parasites in the human body. There are a lot of different Zappers out there, but the main thing is you want it to be positive offset. Here is a qoute from Dr. Clark -
"Subsequent testing showed it was not due to some unique design, or special wave form produced by the device. It was due to battery operation! Any positively offset [DC] frequency kills all bacteria, viruses and parasites simultaneously given sufficient voltage (5 to 10 volts), duration (seven minutes), and frequency (anything from 10 Hz to 500'000 Hz)."