Contactless magnetic field testers quickly and efficiently test the magnetic field of switches, valves, pumps or individual components. When operated at close range, the device does not need to be opened or any cover removed. The continuous operation is thus secured and servicing times are considerably reduced. These types of testers are commonly used in the automotive and commercial vehicle sector, or in the heating and plumbing fields. The robust, compact design (in the shape of a pen) means they are versatile to use.