We need electricity here; however electrical appliances are pretty simple. A surface defect or a near-to-surface one disrupt a magnetic field inside the object and an indication of medium particle, often fluorescent, can be visible outside. It is more robust compare to liquid penetrants. No such precise cleaning is demanded. Surface may be scratched; even a defect can be covered with thin material layer. Indications are similar to PT, common standards are published. Inspection of steel butt welds is very popular. The best method for bolt thread inspection, a false indication can be eliminated. Complex task of e.g. steel liners built-in aluminium block of an automotive engine can be performed.