hi colin : 2 years ago I bought hulda clarks book"a cure for all diseases" and in her book she descibes how to build your own zapper or frequency generator ,I have made different versions in the past a very basic one that uses a 9 volt battery ,but the battery runs down to quick ,and I have made a version that you can plug into a household outlet which works very good , I was able to get most of the supplies from radio shack and will take about 6 hours to put together ,you will have to do a little bit of soldering on the circiut board , my version cost about $30.00 bucks to make ,I have seen the same versions on the web already made almost $200.00 , as far as how it works I think that it is a very simple and effective way to kill parasites , viruses ,and bacteria , I have avoided many cold and flu outbreaks since using it , but can be uses for many other illnesses , the only drawback is you should not use it if you have amalgams ,because it will mobilize the murcury in the amalgam fillings because of the low volt dc current other than that it is very effective