a Clark Zapper has a slight stimulatory effect on immunity.
A Beck Zapper directly kills bacteria and disables viruses.
a Rife Zapper is a new age toy riding on the coat-tails of the Royal Rife story although its design is too dissimilar.
a biofeedback device has no effect on the body because it is basically just responding to the resistance of the skin as it changes with stress.
a mihealth is a Pulsed Magnetic Field (PMF) device that reduces stress and has a general positive benefit on the body.