The cellphone battery case, or “introspection engine” is designed for the iPhone 6 to monitor the electrical signal sent to its internal antennas.
Snowden and Andrew Huang, a hardware hacker, presented the design before an audience at the MIT Med Lab in Boston, Massachusetts on Thursday, according to Wired magazine.
The battery case comes with a small mono-color screen and tiny wires that slot into the iPhone’s SIM-card slot to test points on the phone’s circuit board.
There the wires read electrical signals sent to the phone’s two antennas that are used by its radio, including GPS, Bluetooth, WiFi and cellular modem. The battery case will then warn the user through an alert message or an audible alarm if its radios are transmitting anything when they are meant to be off.
The purpose of the device is to offer the cellphone owner a check on whether the phone’s radio is transmitting, a concern for those wanting protections from hackers or for reporters wanting protections from government surveillance in hostile foreign countries.
“One good journalist in the right place at the right time can change history,” Snowden told the MIT Media Lab crowd via video stream, according to Wired magazine. “This makes them a target, and increasingly tools of their trade are being used against them.”
Snowden speaking via video stream said the add-on is more trustworthy than the “airplane mode” which has been shown can be hacked or spoofed.
“Our approach is: state-level adversaries are powerful, assume the phone is compromised,” Andrew Huang told Wired.
For the purpose of Thursday’s presentation the hardware is still in its design stage. The pair plan to develop a prototype over the next year, and then create a supply chain in China.
Snowden and Huang then plan to offer the devices to journalists and newsrooms.
Huang told Wired that when reporters are overseas in places like Syria or Iraq, “those [governments] have exploits that cause their phones to do things they don’t expect them to do.”
He added “You can think your phone’s radios are off, and not telling your location to anyone, but actually still be at risk.”
Huang said turning off your phone with its power button can still be hacked with clever malware and even placing it in a Faraday bag designed to block all radio signals can still lead to leaked signals.