How do you steal intellectual property from a 3D printer? Just listen very closely.

Researchers at the University of California, Irvine have revealed a security weakness in the 3D printing process -- sound waves.

Scientists designed a program capable of recording and analyzing the sounds emitted by the printer's moving parts. Once decoded, the sounds -- each connoting a precise movement -- can be used to reverse engineer the product being printed.

Scientists at UCI's Advanced Integrated Cyber-Physical Systems Lab say the program could installed and used on a smartphone.

"In many manufacturing plants, people who work on a shift basis don't get monitored for their smartphones, for example," researcher Al Faruque said in a press release. "If process and product information is stolen during the prototyping phases, companies stand to incur large financial losses. There's no way to protect these systems from such an attack today, but possibly there will be in the future."

Faruque and colleagues were initially studying the relationship between information and energy flows in 3D printing systems. Printers emit energy in the form of sound waves. Researchers realized these acoustic signals could reveal significant information about the manufactured product.

"Initially, we weren't interested in the security angle, but we realized we were onto something, and we're seeing interest from other departments at UCI and from various U.S. government agencies," said Faruque.

Of course, most of today's 3D printers aren't making top-secret objects. But as 3D printing becomes a larger part of the U.S. economy, that could change.

"President Obama has spoken about returning manufacturing to the United States, and I think 3D printing will play a major role because of the creation of highly intellectual objects, in many cases in our homes," Faruque added.

Researchers have begun to think about ways to disguise a printer's acoustic signals -- blocking them out with white noise or shrouding them in random signals -- but for now, Faruque says the best way to protect intellectual property inside 3D printers is to keep smartphones away.