You can do that from EEG. You usually get an API which exposes a number of wave "channels". Depending on the person, if you for example make your hand into a fi

You can do that from EEG. You usually get an API which exposes a number of wave "channels". Depending on the person, if you for example make your hand into a fist, you might get an isolated spike on one of the channels. When developing custom controls based on these signals it's difficult to find actions that will make a channel or combination of channels spike consistently, but you may end up with like, "press tongue to top of mouth" for yes, "make right hand into a fist" for no kinds of things. This is from some minor diy experimentation a few years ago, might be out of date.