Little SecretJust like telescopes watching distant stars, a strong audio recording, when we spontaneously think of something we make these little movements in the mouth. All it takes is to keep the chin squeezed or otherwise your mouth immobile, and they can't use audio recording to be aware of your thoughts anymore.
If you want to avoid your thought process being listened to, just keep your mouth immobile, chin squeezed, no movement of tongue, etc.
...don't trust me. Put this into observation in cases where you feel like being peculiarly deceived by people.
If you are business man, maybe they sent someone to seduce you, rephrasing your opinions so that they appear similar to you and you start dating them.
If people say it is a brain decoding device I think it is a lie, humanity was claimed to know about 1% of brain activity anyways, so that would be very difficult to develop.
I think it is a little trick that's been around for few decades already.