Stephen, thanks for the informative post. Have seen and read about FSCAN equipment on various sites but until your post I had not yet quite figurred out exactly what their intended purpose is. I had been thinking of them only from the perspective that they can be used for a variety of souped-up zapping applications; hadn't thought of them as a detection/monitoring tool. Thanks for educating me. Are you familiar with Dr. Clark's Zincrometer?
Her 2004 revised edition of CureForAllDiseases includes a "how to build a Zincrometer" parts list, which does not involve any chips. The reason why is that the Zincrometer itself is an audio oscillator circuit and while it does not have a built-in frequency generator it can be coupled to an external one for those applications that require frequncy generation. She offers her own called MiniFG and her products page sells a package that includes a MiniFG and a Zincrometer. This document provides her explanation of these.