Magnetometers are devices that measure magnetic fields. A magnetometer is an instrument with a sensor that measures magnetic flux density B (in units of Tesla or As/ m2). Magnetometers refer to sensors used for sensing magnetic fields OR to systems which measure magnetic field using one or more sensors.Since magnetic flux density in air is directly proportional to magnetic field strength, a magnetometer is capable of detecting fluctuations in the Earth's field. Scalar magnetometers that measure only the magnitude of the vector passing through the sensor regardless of the direction. Quantum magnetometers are an example of this type of magnetometer. Various magnetometers used to measure magnetic fields are discussed in following sections.