A gaussmeter, also known as a magnetometer, is a device used to measure the strength and direction of a magnetic field. Small, hand-held versions are available and the user can carry it with him to monitor magnetic fields as he walks. The device may also be referred to as an electromagnetic field detector, or EMF detector for short. The device has several scientific uses and is popular among paranormal researchers.

Two types of gaussmeters exist: scalar and vector. The scalar gaussmeter measures the strength of the magnetic field present in the area around the device. The vector gaussmeter measures the direction of the magnetic field depending on where the device is and which direction it's pointing. A gaussmeter may combine both of these technologies.

Using a gaussmeter is a fairly simple process. The screen provides a reading of how strong the magnetic field is and may indicate the direction it’s coming from. If the person holding it walks closer to the magnetic source the reading will rise; it will lower if the person walks away from the source. Multiple sources can create conflicting readings, however, and may require more advanced technology to determine where the sources are coming from.

Changes in the magnetic field depend on where the user is and the strength of the Earth’s magnetosphere in that particular area. The sun interacts with areas of the magnetosphere differently and the strength of the signal can fluctuate with the sun's activity. Certain natural materials, such as specific rocks or rock formations, may also interfere with the gaussmeter's reading.

Today, gaussmeters serve a number of uses. They are a valuable tool in space exploration for learning more about the magnetism of foreign planets and other bodies in space. Here on Earth, they can detect certain landscape formations and for this reason are used in geophysics to get an idea of how the land is laid out. Certain magnetometers can also detect hidden items such as shipwrecks and are at work in metal detectors used both by beachcombers hunting for lost items in the sand and by security teams to detect guns or other weapons.

The magnetometers are gaining popularity in cell phones as well. A phone utilizing this technology can point out directions to the user much like a compass does. It also may be used to let the user interact with the phone without actually touching it. Though still in the beginning stages of development, a magnet can be used to interact with the magnetometer in the phone. The magnetometer can pick up information about how the user is turning or moving her hand and then the phone responds to these movements.