It looks like an external battery case with a small mono-color screen and is being described as an "introspection engine." The device's tiny probe wires have to attach to test points on the iPhone's circuit board, which are accessible through the SIM card slot. The phone has two antennas that give off electrical signals and they're used by its radios, including GPS and Bluetooth.
The probe wires read the radio's electric signals, and by doing so the modified phone warns you when these signals transmit information when they're meant to be off. You'll instantly receive alert messages or even an audible alarm, and the phone can even shut off automatically. The intention here is to allow reporters to carry their phones into hostile foreign countries without revealing their locations to government-funded adversaries. They'll still be able to record video and audio while their iPhone's
radio signals are disabled.
However, the device is still nothing more than a design for now. Snowden
and Huang are hoping to build a prototype over the next year, and eventually start offering these modified iPhones to journalists.