Most of those supposed EEG sensors are just sending the forehead or facial muscles which are quite thick and noisy, electromagnetically. When you focus, you ten

Most of those supposed EEG sensors are just sending the forehead or facial muscles which are quite thick and noisy, electromagnetically. When you focus, you tend to tense your muscles, so these devices work to a limited extent. But they are not EEG, especially without a conductive lubricant to get through the skin.