Microcontrollers Are Ultra-Low-Power Radios

Modern electronics rely on digital communication protocols such as SPI, UART, I2C, and I2S for inter-IC communication, all of which operate on square-wave signals. We show that these ubiquitous lines, when cleverly manipulated, can be exploited for wireless communication over distances exceeding one hundred metres. NoLoRa leverages the fact that square waves are rich in odd harmonics , by carefully timing data patterns streamed through high-speed SPI/I2S interfaces, higher-order harmonics naturally fall within the LoRa ISM band, allowing a standard microcontroller to transmit fully LoRaWAN-compatible signals to commercial gateways without any dedicated RF hardware. Complementing this, ZeroScatter-LoRa exploits the internal PMOS and NMOS transistors of MCU I/O pins, whose inherent impedance switching can be modulated with a LoRa chirp waveform, enabling the microcontroller to backscatter an incoming carrier and function as a passive RFID tag with zero added components. While these findings reveal a critical electromagnetic security vulnerability in modern digital systems ,where unshielded I/O lines can act as unintended antennas our work harnesses these phenomena constructively, demonstrating a new frontier for ultra-low-power wireless communication consuming only tens of microwatts.