Typically, there are three types of metal that a detector can sense: ferrous, non-ferrous and stainless steel.
Ferrous metals – These types of contaminant are both magnetic and conductive, which means they are easily sensed by standard metal detectors.
Non-ferrous metals – Although non-ferrous metals are not magnetic, the fact they are conductive means that they too can be easily detected with the right detector model, properly installed.
Stainless steel – generally considered a ferrous metal, but one that is high in chromium. It is the most difficult to detect as it is neither magnetic nor conductive. Stainless steel is even more difficult to find when the product contains water or has a high salt content.