A new brain-computer interface device can translate the neural signals controlling someone's vocal tract into full sentences of audible speech.
Now think of this out in the wild. It may be for those who can't really speak for themselves at the moment, but I can see certain parties forcing others to wear something like it to keep track of what they've thinking. Fortunately, at the moment it can really only handle those who sort of mumble, but with further development the machines' capability could extend to actually translated the thoughts that don't get "voiced".
In free societies this is likely to be strictly regulated. In despotic, Saudi Arabia for instance, widely embraced. And even where rights are respected there will be those who cheat.
But then it is very likely that most despots will soon learn that you just can't keep track of everyone's thought. They'll have to focus on those they have reason to suspect.
And it just occurred to me that we will be seeing scams claiming that parents will be able to eavesdrop on the thoughts of their teens. More tension and strife, just what families don't need.