An Electromagnetic field meter or EMF meter as it is usually known  is a device designed to reveal and calculate electromagnetic radiation in the surrounding area. It is a popular tool used by ghost hunters, often the first piece of equipment they invest in. It is believed to be able to detect the presence of paranormal activity.  An EMF meter is used in a myriad of settings, including industrial, scientific, and medical fields, as well as in more personal and intimate settings, such as the home.

In a paranormal research capacity, the device is used to detect and measure electromagnetic radiation that is believed to be produced by entities of a supernatural nature.

The theory behind using an EMF meter is that ghosts are made up of energy and that they can manipulate or emit electromagnetic fields, therefore making the meter a valuable ghost detecting tool.

There is also scientific evidence to support this. Electromagnetic fields are generated by electrical activity in the brain and nervous system, in the body. Electrical appliances and power lines also generate this. It is widely believed that ghosts may be able to influence or manipulate these fields, creating disturbances that can be detected by electromagnetic sensors.

So if a person suspects paranormal activity in a particular place, an EMF Meter can add additional evidence to an investigation.