Electromagnetic field (EMF) detectors are very useful tools provided they are used properly. There are instructions with each type that you should read. These meters detect fluctuations in Electromagnetic fields. EM fields are normally generated by electrical appliances and other items such as computer monitors, cell phones, etc. They are also created by the weather in outer space such as geomagnetic storms and solar flares. When you find an unexplainable field, normally between 2 to 7 milligauss, it is associated with spirit activity. These meters are will not always detect a spirit present, but they are another helpful tool is tracking ghosts. EMFs are measured in units called milligauss.