Reminds me of how the first generation iPod firmware and keys were reverse engineered. They blinked out bit patterns on the LCD backlight and used a camera to read the data in! https://mastodon.social/@bagder/111538350617290554
Citation needed, but I think I read that hackers dumped the firmware of Canon cameras by blinking the single red LED on the camera (and foregoing the main graphical LCD). See the CHDK and Magic Lantern projects.