Uncanny Atlas
Tool

EMF meter

A handheld meter that ghost hunters carry to look for changes in electromagnetic fields that they link to spirits.

What users say it does
McGill University's Office for Science and Society says users believe ghosts give off or disturb electromagnetic fields, so a meter that lights up may mean a spirit is near. Benjamin Radford writes that some hunters, the Ghost Hunters team T.A.P.S. among them, hold that strong magnetic fields can cause hallucinations that people take for ghosts.
What it measures
Wikipedia says an EMF meter reads alternating-current fields, mostly produced by wiring and other man-made sources, while gaussmeters and magnetometers read direct-current fields such as Earth's own. The National Institute of Environmental Health Sciences describes these fields as invisible energy tied to electric power and lighting.

Benjamin Radford reported for Live Science that ghost hunters rank EMF meters among their most common devices, and that Tom Cook, whose British firm TomsGadgets.com sells paranormal kits, offered starter kits from £105 up to £500 for a custom kit.

In Skeptical Inquirer in 2017, Radford traced the hallucination idea mainly to Michael Persinger, a Canadian neuroscientist, who found that strong fixed-pattern electromagnetic fields aimed at certain parts of the brain could trigger hallucinations, including the sense of leaving one's body.

Sources