I used to work in this field decades ago. It was relatively straightforward. You could see it with your plain eyes in the EEG, but also you could calculate metr

I used to work in this field decades ago. It was relatively straightforward. You could see it with your plain eyes in the EEG, but also you could calculate metrics from it. One really fun way was to listen to the sped up EEG signal when a person is put into anesthesia. It sounded like you went underwater. The key thing is that when people are given muscle relaxants, you need an independent method to measure consciousness directly. I haven't followed this in decades so it's a total surprise to me if it isn't mainstream yet. You could buy a module for your anesthesia monitor for this, no need to use a separate device.