Scientists have developed a battery-free wireless 2-channel EEG system powered by a hybrid power supply using body heat and ambient light which could be used to monitor brain waves after a head injury or for other applications. The hybrid power supply combines a thermoelectric generator that uses the heat dissipated from a person’s temples and silicon photovoltaic cells. The entire system is wearable and integrated into a device resembling headphones. The system can provide more than 1mW on average indoor, which is more than enough for the targeted application.