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Are there things in your house that go bump in the night? Unexplained sightings or premonitions that something unearthly is in your room? A new iPhone accessory called Mr. Ghost can now help you confirm the unknown by detecting the levels of electromagnetic radiation—whether under your bed, in the walls, or coming from one of your appliances—that are all around. And yes, that could, theoretically, include the presence of ghosts.

The brainchild of computer scientist and inventor Aaron Rasmussen (CAS’05, COM’05), the Mr. Ghost electromagnetic field (EMF) detector measures electromagnetic fields that are generated by electrons moving through wire (like in an appliance’s power supply).

Ramussen got the idea for the detector last spring when he began thinking about how much society now depends on smartphones—for such things as a GPS and an alarm clock and for email and phone calls. Having programmed for smartphones in the past, he remembered an electroscope he had played with as a child that detected static charge.

“I guess that experience stuck with me,” says Rasmussen, whose latest project grew out of a desire “to push the smartphone further.” Creating an EMF detector, he says, was one way to do that. He also thought it would be fun to create something that would allow people to learn about the unseen world that exists all around them.

Here’s how Mr. Ghost works: the EMF detector is an attachment that looks like an old cordless phone antenna. Once you’ve plugged it into your iPhone, iPad, or iPod headphone jack, the free Mr. Ghost app opens. Users can wave the device around the areas they want to test and the screen will display any spike in EMF signals.

“The app even lets you record the signal so you can listen to it later,” Rasmussen explains in a video he made for the project. And the “ghost-hunting,” or gyro, mode “lets you swing the detector back and forth and see where the different radiation sources are.”

In the video above, Aaron Rasmussen demonstrates how Mr. Ghost works.

Rasmussen, who is based in Los Angeles, soldered together the first prototype of Mr. Ghost himself. He made engineering drawings of the antenna shape and brought them to a local machine shop, where the antenna was milled out of aluminum. He formed a silicone mold of the aluminum shape in his kitchen, filled it with urethane-casting resin mixed with pigments, and inserted the electronics. At that point he demolded the antenna, and voilà!—a device that would aid even the most intrepid ghost hunter.

With a dual major in computer science and mass communication, Rasmussen had already created several inventions, including a robotic sentry gun capable of tracking and shooting any moving target via an electronic eye, quirky energy drinks, and a video game that lets people experience what it’s like to be blind. He knew that he needed a catchy name for his new invention, since few people would know what EMF stands for. Since any device detecting electromagnetic fields can theoretically be used for ghost hunting, Rasmussen decided to name it Mr. Ghost, figuring the name would catch people’s attention.

Mr. Ghost took off after Rasmussen set up a page on Kickstarter to fund the device. He had previously used Kickstarter successfully to fund development of his video game. He promised to ship Mr. Ghost to anyone who pledged $20 or more. After posting the project to Kickstarter in late November, in just two weeks Rasmussen raised more than $35,000 from 1,439 supporters. When the orders started coming in from Kickstarter, he teamed up with a manufacturing company to mass-produce the units.

Right now, only those who have contributed money to the Kickstarter project can get a Mr. Ghost, but plans are in the works to sell it in stores. Rasmussen has already set up a company, Protagonist, to market the iPhone accessory.

He says that feedback from early users has been overwhelmingly encouraging. “One guy bought one for his nephew because he wanted him to have more science in his life, and a few users have one and now want a couple more,” he says. “But I’ve yet to hear from anyone who has found a ghost.”

Does Rasmussen believe in ghosts? He describes himself as “an open skeptic,” but says he’s prepared to be persuaded otherwise. “If the users of Mr. Ghost are out there measuring electric fields, maybe that is a way to find evidence of ghosts. What I like about my invention is that it allows people to get a more accurate view of their environment.”