In academia, paranormal scientists are often disparaged for advocating the use of state-of-the-art technology to capture ghosts. Today's TV shows and YouTube are filled with gadget-toting scientists hunting ghosts and spooks, such as Ghost Hunters.
Due to the lack of a physical "theory" for how or why ghosts may exist, they are considered pseudoscience. As a result, it's difficult to prove - or disprove - their existence. But enterprising scientists and technologists have never stopped trying to figure out ways of detecting them throughout history. In most cases, these attempts are based on folklore accounts of ghosts to determine what kinds of traces they might leave behind. The trendy thinking when it comes to developing ghost hunting technology is: figure out what kinds of physical clues a ghost might give that it was there, then build machines that can recognize it. Detecting the inherently ethereal using science is no doubt a paradox, which necessitates this approach.
A ghost or spirit living in our world suggests an interaction between the realm of matter and the realm of the metaphysical. Metaphysical existence cannot be quantified, so any scientific approach would have to study the residues left behind in the physical world by undead souls (hypotheses such as panpsychism exist to explain the existence of one immaterial substance: consciousness). Simply put, if you want to prove that an invisible man is walking around a room, you won't see his feet. However, you might hear his footsteps and find his footprints. It is obvious, however, that an invisible man is not the same as a ghost, since a human being is still flesh and blood. In the absence of knowledge of what a ghost is made of, ghost hunters must make guesses regarding how they might affect their immediate surroundings. Thus, even when ghost hunters use legitimate scientific equipment, they're speculating rather than knowing what to look for.
Detectors of electromagnetic fields (EMFs) are a suitable example. Ghost hunters use these devices frequently to search for anomalies that indicate paranormal activity. There are two types of electromagnetic radiation sought by ghost hunters: ionizing and non-ionizing. In certain contexts, they argue that these radiations may indicate the presence of an otherworldly presence. However, the data picked up by those detectors can often also be explained by mundane factors. The presence of EMF can be found almost anywhere, and unusual EMF detections are more likely to reflect incomplete scientific understanding.
The mere fact that people feel haunted in a place with EMFs does not prove there is a haunting there. Researchers have found that certain types of EMF exposure can cause physical and psychological side effects like paranoia, nausea, and the belief that one is experiencing profound events. In the 1980s, a Canadian psychologist named Dr. Michael Persinger created a famous "God Helmet" placed around a subject's head to emit electromagnetic energy. The temporal lobes of the wearer were bombarded with EMFs once the helmet was activated. The majority of people who experienced this reported feeling some kind of presence in the room with them, including sometimes seeing God.
It is also possible that infrasound, which paranormal investigators have also claimed is a sign of ghostly activity, is having a similar effect. As audio frequency ranges below the normal human hearing range, low-frequency infrasound can have a seemingly enigmatic effect on our minds and bodies. Infrasound can be produced by anything from the movements of tectonic plates beneath our feet to the rumble of thunder clouds in the sky. Noise exposure can cause headaches, dizziness and nausea, as well as psychological effects like anxiety and dread, depending on the source and nature of the sound. There is evidence that infrasound contributes to paranormal perceptions, or at the very least reinforces them.
Other popular ghost-busting technologies exist as well. Night vision goggles, infrared cameras, and sensitive microphones can all be used by ghost hunters to discover the presence of ghosts in the dark. They can also use infrared cameras and sensitive microphones that measure ambient temperatures. As opposed to Ouija boards, dowsing rods, and Ghost Boxes, these are considered more scientific instruments. The problem with all of them, however, is the same as it is with infrasound detectors and EMF detectors. Rather than empirically and repeatedly demonstrating facts that have yet to be accepted, they are being used based on guesses about what hypothetical ghosts might do. Hence, there is an urgent need for further paranormal research.