tl;dr: Researchers have discovered an undocumented feature in several ESP32 chips that allows firmware to bypass the fixed WiFi/Bluetooth radio and capture raw IQ baseband samples, effectively turning them into SDRs covering 2.2–2.7 GHz (and 4.8–6.0 GHz on the ESP32-C5) at up to 80 MS/s. Bandwidth limits mean most chips can only export snapshots for spectrum analysis, though the ESP32-S31 can stream continuously over Gigabit Ethernet. Independent projects have leveraged the finding for phase-coherent direction finding (ESPARGOS), a general-purpose SDR with an FPGA frontend, and a 5.8 GHz FPV video receiver (C5VRX).