How do our simple circuit and wire probes compare to a water/moisture detection module that you can find on retail sites such as eBay? These products typically contain a probe of some sort, plus a small electronic module. A picture of one of these modules, plus a few probes, are shown here:
The three probes pictured each have two terminals and are simply an exposed copper trace on a circuit board, analogous to the exposed wires we saw in our circuit in Figure 9.8. A key difference is that these probes expose a larger surface area and are therefore more sensitive. Furthermore, they are also likely to be less prone to corrosion (at least in the short-to-medium term) than two stripped wires.
Let's discuss the electronic...