Limor Fried '03, MEng '05, was on the train from New York City to Boston recently when the woman next to her called a friend on her cell phone and began chatting about uncomfortably intimate matters. They were traveling in a designated quiet car, where phone calls and loud conversations are verboten. But even though the woman hung up when the conductor asked her to, she soon placed another call, again regaling fellow passengers with the gory details of her personal life. Fried, who studied computing culture at the Media Lab, decided to take action. She surreptitiously pressed a button on a pocket-sized gadget she'd designed as an MIT grad student. Fried's so-called Wave Bubble jams cell-phone reception by creating destructive radio frequency interference. When the chatty woman's call suddenly dropped--and her repeated attempts to reconnect mysteriously failed--she finally opened a book and began reading, silently.

Fried's frustration at having to listen to other people's phone calls led her to create the Wave Bubble as part of her master's thesis. But she's no lone vigilante. In fact, she freely shares the design of her secret weapon with anyone else who wants to rid public spaces of intrusive cell-phone conversations. She posted instructions and a parts list for her gadget online, enabling anyone to make a cell-phone jammer--with the caveat that it's illegal to use one. And by sharing the design on the Web, she neatly sidestepped the U.S. Federal Communications Commission's prohibition on distributing the devices themselves.

Today, Fried remains committed to the idea of sharing her designs--and her engineering expertise. She runs her own company, Adafruit Industries of New York City, through which she sells kits that allow people to undertake less subversive projects, such as making an iPod battery-pack charger and transforming a bike wheel into a customized LED display. All her kits are based on designs that can be modified or improved by her customers. She also finds time to host an Internet video program, called Citizen Engineer. In a recent episode, she and cohost Phil Torrone explained how cell-phone SIM cards (the chips that identify a user's account and network) work and how to hack them to, say, recover deleted text messages.

"I'm helping people learn electronics," Fried says, "and also ensuring that the information will always be available." And when users adapt and enhance her designs, she says, it helps make her products better.

Fried isn't the only one freely sharing her projects and knowledge. In fact, open-source hardware, as it's called, is increasingly popular among all types of engineers, from students and hobbyists to entrepreneurs to engineers at large companies like Sun Microsystems and Nokia. The basic idea is that if the parts and designs for devices--and electronics are only one example--are available to the public, then more people can modify the designs to fit their specific needs. By posting designs online, hardware engineers have found a huge community of consumers and fellow professionals who are willing and able to provide feedback, and even to extend the designs in ways their creators hadn't thought of. In effect, the open approach to hardware design can serve as a massive, distributed research-and-development effort, and even a quality assurance program on the cheap.