Can technology track down spirits?

A movie celebrating the antics of a paranormal investigation agency spawned a popular catchphrase in the mid-'80s. But forget the proton packs and the deionizers. Tonight on "Tech Live," we got the real thing. So, who you gonna call?

The Presidio of San Francisco is one of the city's hot spots, known for its panoramic view of the Golden Gate Bridge, rich military history, lush forests -- and ghosts.

Mia Andrade, manager of the Lost Ladle Cafe, is convinced she's not alone, even when she's the only person in the former military post's Officers Club.

"From the corner of my eye, I caught a green blur. It could have been a man in a green uniform, in a coat, which some people say they have seen before," she said.

She is not alone. Others have reported sightings of men in old war uniforms and the sound of loud knocks from deserted rooms at the former Army post, which became part of the Golden Gate National Recreation Area in 1994. In addition to the United States using the area as a post from 1848 to 1994, the Presidio served as a military post under the flag of Spain from 1776 to 1822 and of Mexico from 1822 to 1848.

Hunting ghosts

Parapsychologist Loyd Auerbach has known about the "hauntings" at the Presidio since 1999, when he and a team of paranormal investigators toured the grounds.

Today, armed with a TriField Natural EM Meter and a tiny pad of paper, he wanders around the ballroom, assessing the moves of the needle as it jumps and spikes.

"What we have here is an unusual reading. We have an anomaly in the environment," he said as he moved the meter from ceiling to floor.

Tool of the trade

The TriField Meter is a magnetometer that measures variations in magnetic fields. It was originally designed to detect environmental pollution, but Auerbach discovered its usefulness for paranormal sleuthing.

As a professor of the paranormal, he investigates supernatural occurrences with the help of the TriField Meter, and usually works in conjunction with a team of paranormal specialists.

"The technology was always to see if there were any environmental disturbances or if there was a physical something that we could measure that connected to the human experience. But it was always about the human experience," he said. "You wouldn't walk into a place just because it looks spooky to see if you could measure something with technology. You'd have a story first."

The tech comes in to verify the witness' accounts.

Decontructing apparitions

Ghosts, he says, are fields of energy -- a consciousness field. "Kind of like some of the aliens in 'Star Trek,'" he added.

Auerbach operates based on the assumption that changes in geomagnetic fields affect people's psychic ability. And being psychically aware, Auerbach says, is tied to seeing ghosts.

"It's been suggested in these cases that the energy affects the magnetic environment. In other words, that there is magnetism in the environment," he said. "By moving something energetic through the magnetic field, you change the magnetic energy. You change the pattern. You pick something up."

As Auerbach lifts his meter in a corner of the ballroom, an unexplained force spikes the magnetic level as detected by the device.

"Not only spiking, but it's looking like it's fluctuating wildly, which is pretty unusual," he said.

Do they really exist?

But just because something registers on the meter doesn't mean it's a ghost.

"The readings themselves with a single device like a TriField Meter means very little," he said.

He says that there could be other causes for the spike that we are unaware of. Indeed, Auerbach says, the very definition of a ghost has been a hot topic of debate.

"It's a consciousness without a human body," he said. "We have, in science, a dispute going on as to whether consciousness even exists in the body, let alone after death."

"We have no devices that can physically detect human consciousness where we know for a fact it should be, let alone something that's going to be wandering around that we can't see," he said.

It's a parapsychological assessment of what remains essentially a mystery to the living.

Still, Andrade knows she felt some unexplained presence, which still haunts her.

"Even though I've never made direct eye contact, I definitely know that something is there," she said. "There have been too many unexplained experiences. So, in my heart, I think there are ghosts here."