Edward Snowden's New Research Aims To Keep Smartphones From Betraying Their Owners (theintercept.com)

Smartphones become indispensable tools for journalists, human right workers, and activists in war-torn regions.

 But at the same time, as Intercept points out, they become especially potent tracking devices that can put users in mortal danger by leaking their location.

 To address the problem, NSA whistleblower Edward Snowden and hardware hacker Andrew "Bunnie" Huang have been developing a way for potentially imperiled smartphone users to monitor whether their devices are making any potentially compromising radio transmissions.

"We have to ensure that journalists can investigate and find the truth, even in areas where governments prefer they don't," Snowden told Intercept.

"It's basically to make the phone work for you, how you want it, when you want it, but only when." Snowden and Huang presented their findings in a talk at MIT Media Lab's Forbidden Research event Thursday, and published a detailed paper.

From the Intercept article: Snowden and Huang have been researching if it's possible to use a smartphone in such an offline manner without leaking its location, starting with the assumption that "a phone can and will be compromised." [...] 

The research is necessary in part because most common way to try and silence a phone's radio -- turning on airplane mode -- can't be relied on to squelch your phone's radio traffic.

Fortunately, a smartphone can be made to lie about the state of its radios.

The article adds: 

 According to their post, the goal is to "provide field-ready tools that enable a reporter to observe and investigate the status of the phone's radios directly and independently of the phone's native hardware."

 In other words, they want to build an entirely separate tiny computer that users can attach to a smartphone to alert them if it's being dishonest about its radio emissions.

Snowden and Haung are calling this device an "introspection engine" because it will inspect the inner-workings of the phone.

 The device will be contained inside a battery case, looking similar to a smartphone with an extra bulky battery, except with its own screen to update the user on the status of the radios. 

Plans are for the device to also be able to sound an audible alarm and possibly to also come equipped with a "kill switch" that can shut off power to the phone if any radio signals are detected.

Wired has a detailed report on this, too.