Musk is trying to do it with an implant.

Facebook is trying optical imaging to convert inner-speech into text.

https://techcrunch.com/2017/04/19/facebook-brain-interface/
>The team plans to use optical imaging to scan your brain a hundred times per second to detect you speaking silently in your head, and translate it into text.

What are some other ways inner-speech could be captured and sent to a computer?