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Edward Snowden is designing a device that will warn you if your phone is spying on you.
Frederick M. Brown—Getty Images

Three years after Edward Snowden rose to fame as a whistleblower who exposed government surveillance, the former NSA contractor is working on a device that will let you know if your phone is being hacked.

Along with hardware hacker Andrew "Bunnie" Huang, Snowden presented a design at the MIT Media Lab Thursday for a device similar to an iPhone case that will track electrical signals sent to the phone's internal antennae, Wired reports. The contraption will constantly check whether your phone radios are transmitting—and potentially silently activating your microphones or cameras.

The so-called "introspection engine" would look like an external battery case, but would actually contain tiny probe wires that would snake inside the iPhone to attach to points on the phone's circuit board. Those wires would transit electrical signals to the two antennas in the phone used by radios like GPS and Wi-Fi. The modified phone would then be able to warn users if the radios transmit any signals when they're supposed to be out of use.

Snowden and Huang say their product will offer strong privacy guarantees for people looking to shield their devices from antagonists with especially developed hacking and surveillance capabilities. Someone who might benefit from the device, for instance, is a reporter trying to carry his device into a dangerous foreign country without giving away his location.

"Our approach is: state-level adversaries are powerful, assume the phone is compromised,” Huang told Wired. "Let’s look at hardware-related signals that are extremely difficult to fake. We want to give a you-bet-your-life assurance that the phone actually has its radios off when it says it does."

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The creators promise that the device will be far more effective than if you simply turn off your iPhone or place it in a Faraday bag, which is designed to block all radio signals. Advanced malware can make an iPhone appear to be turned off when it's not, and Faraday bags can still leak radio information, Snowden and Huang say.

Unfortunately, it will be a while before this new technology becomes available. Snowden and Huang say the iPhone add-on is just in its planning stages. They hope to develop a prototype in the next year and develop a supply chain in China of modified iPhones for reporters.