The current boom is based on an instrument that has been deployed in hospitals for decades – the electroencephalograph - aka the EEG. It is used to detect brainwaves, for example the alpha waves that generally correspond to relaxation, or the beta waves that indicate alertness. The new wave of firms has produced headsets that are essentially cheaper, easier-to-use versions of EEG machines, and also do not need gloopy conductive gel to operate. The Neurosky headset, for example, only has one sensor as opposed to around 20, and is thus slightly less accurate.
