In some embodiments, an electronic device for monitoring EEG data, may include one or more of the following features: (a) a housing, (b) a processor disposed within the housing, (c) at least one sensor operatively connected to the processor, (d) at least two EEG electrodes operatively connected to the processor and positioned on the housing for receiving EEG signals from an ear surface, and (e) a plurality of EEG electrodes, wherein the processor measures the impedance of the plurality of EEG electrodes.
