most zappers run on 9V batteries and the average level of current that goes through the electrodes is around 5-6V. It's enough to give you a mild sensation if you touch your tongue to both terminals.
Of course, everyone is entitled to their opinions, but if you want more information on zapping, Hulda Clark e highly recommends them and discusses them in her books, Don Croft is another proponent: http://www.worldwithoutparasites.com . I'm sure if you googled or checked the zapping forum on cz you'd also find tons more info.
Zapping has done wonders for helping get my candida under control. it's also beneficial for killing off bacteria, viruses and parasites in the body, thereby giving your immune system a HUGE boost which in turn helps minimize allergic reactions.