Every speaker can be used as a microphone if the circuitry is added to do so.

Many common SOC's MediaTek, Realtek, and Broadcom SOC's quite often used modern audio capable devices analog pins can be software defined either input or output.

IIRC I saw already Bruce Schneider's blog some team proof of concept where they listened using laptop speakers what was spoken in that room. Audio quality wasn't perfect, but it making sense what was spoken was good enough.

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