Magnetsökare.

Var var det magneterna var? De ligger under vägen.

Magnetsökaren hittar dem till dig.

"This magnetic field detector consists of a sheet with nickel particles in a gelatinous suspension.
The flux detector will be darker in color when the magnetic field is perpendicular to the foil (Near the poles North and South), and it becomes lighter when the magnetic field runs parallel to the foil.
Ideal for detecting magnets in MagnoRail system or StreetSystem."