Online magazine Motherboard have recently uploaded a video on YouTube where a reporter interviews white hat hacker Ang Cui. Cui is the inventor of the Funtenna which is software malware that can infect any embedded device, turning it into an improvised RF transmitter.
As an example of the type of devices the Funtenna can infect, Cui shows how he infected a desktop telephone, as well as a desktop printer. The malware running on the phone causes the phone to transmit an RF signal of the voices heard by the microphone, and the malware running on the printer causes the printer to emit a binary coded transmission of the text being printed. The malware is able to do this by forcing a GPIO, PWM or UART interface on the printer to modulate in a similar way to what is done with the Raspberry Pi FM transmitter project, rpitx. To receive and decode the signal Cui uses a software defined radio and a GNU Radio program.
Ang Cui previously presented his work on Blackhat 2015 and his slides can be found here, and we also show the video of his presentation below in the second video.