Magnetometer

A magnetometer is a measuring instrument used to measure the strength and, in some cases, the direction of magnetic fields.

The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in the 19th century included the Hall Effect which is still widely used. Magnetometers can be divided into scalar devices which only measure the intensity of the field and vector devices which also measure the direction of the field.

Magnetometers are widely used for measuring the Earth's magnetic fields and in geophysical surveys to detect magnetic anomalies of various types. They are also used militarily to detect submarines. Consequently some countries, such as the USA, Canada and Australia classify the more sensitive magnetometers as military technology, and control their distribution.

Magnetometers can be used as metal detectors: they can detect only magnetic (ferrous) metals, but can detect such metals at a much larger depth than conventional metal detectors; they are capable of detecting large objects, such as cars, at tens of meters, while a metal detector's range is rarely more than 2 meters.

In recent years magnetometers have been miniaturised to the extent that they can be incorporated in integrated circuits at very low cost and are finding increasing use as compasses in consumer devices such as mobile phones and tablet computers.

Source : Wikipedia