Where did the idea that EMF meters can detect ghosts come from? Why has it become so widely accepted?
(But seriously, they were scientists and used beepy flashy things to detect ghosts)
This 2005 article states that EMF meters have been used for "ghost hunting" for decades:
[A] major stimulus of today's tech-heavy ghost-hunting trend happened in 1984: The film "Ghostbusters" was released.
...No one really knows what kind of influence a ghost might have on the environment, so ghost hunters try anything and everything.
"If we're doing a full-scale investigation, it goes from the simple electromagnetic-field meters" -- handheld devices that have been ubiquitous on ghost expeditions since the early 1990s -- "all the way to digital video recorder systems with between eight and 12 cameras, depending on the size of the place," said Gloria Young, founder of the Santa Clara group Ghost Trackers. Young also uses a Geiger counter, which measures radiation; motion detectors; barometric pressure monitors; and thermometers.
It goes on to quote a quotes a prominent ghost hunter:
Ghost hunting has grown in the past two decades from a little-known hobby to a much more popular pursuit. Ghost hunters say that, judging from the number of ghost-hunting organizations with Web sites, there are hundreds of groups with thousands of members in the United States.
And technology is a major force behind the trend, said Loyd Auerbach, director and founder of the Office of Paranormal Investigations in the East Bay.
"It was the late 1980s when things began to expand, and part of it was the availability of certain types of technology that we started using in the field," like electromagnetic-field detectors, which start at around $100, Auerbach said. "Part of it was seeing people like me on TV."
There has probably been a recent rise in popularity of EMF meters being used to detect ghosts that tracks the rise in popularity of shows like "Ghost Hunters" where they use the device, among others, to "detect ghosts". Because if you use scientific equipment, you must be doing science, right?
The two featured investigators, Jason Hawes and Grant Wilson, are proudly blue-collar workers, not egghead Ph.D. scientists, which adds to their strong "regular guy" appeal.
...They claim to be skeptics but are very credulous and seem to have no real understanding of scientific methods or real investigation.
But if you're on TV, you have to appear legitimate. From the original cited article:
"If you take the human factor out and just have this instrument, it (seems to) confer some legitimacy -- which these folks desperately want,"
More recently, all-in-one "ghost detector" devices have been released, which I presume are riding the coattails of popular shows such as these.
Is there a scientific reason to think that an anomalous electromagnetic field has anything to do with the supernatural?
No, and ghost hunters themselves cannot cite a single possible theory that EM fields are related to the supernatural. This Live Science article quotes a prominent ghost hunter:
An EMF meter is among the most common devices used by ghost hunters today. I spoke to Tom Cook, of TomsGadgets.com, a British purveyor of "scientific" paranormal kits for the enterprising (and gullible) investigator. Starter kits begin at £105 (US$180) and reach up to £500 (US$850) for a custom ghost-hunting kit. (Negative Ionizer Ghost Containment packs were not listed.)
I asked Cook what, exactly, the scientific rationale was behind the equipment he sold.
"At a haunted location," Cook said, "strong, erratic fluctuating EMFs are commonly found. It seems these energy fields have some definite connection to the presence of ghosts. The exact nature of that connection is still a mystery. However, the anomalous fields are easy to find. Whenever you locate one, a ghost might be present.... any erratic EMF fluctuations you may detect may indicate ghostly activity."
In the final analysis, Cook admitted, "there exists no device that can conclusively detect ghosts."
From the Wikipedia page on Ghost Hunting:
EMF meter: to detect possibly unexplained fluctuations in electromagnetic fields.
Unfortunately in addition to being vague, that line does not cite any sources. So, if one believes (without basis) that ghosts somehow cause "unexplained" fluctuations in electromagnetic fields, the EMF meter would be a valid piece of equipment for hunting ghosts.
Considering the other methods and equipment listed there include dowsing rods, ghost boxes, psychics, clairvoyants and demonologists, it's unlikely that any ghost hunters have commissioned scientific studies into why background EMF levels would fluctuate without an explainable cause.
But really, to a ghost hunter (or TV watcher) an EMF meter is a beeping, flashing device that can "go off" seemingly randomly (though why that might occur is a separate question), which makes things exciting.