Ear-EEG is an EEG acquisition method that record EEG signal from inside the user's ear. This study fabricated an ear-EEG device and tested its ability to detect alpha activity when the subject is in a wakeful relaxation state and its performance in binary auditory P300 BCI system. The ear-EEG fabricated in this study were able to detect the alpha activity from the subjects. In auditory P300 experiment, the highest accuracy and ITR was 95.61% and 2.9685 bits/min, respectively. The surveys given to the participants point out that the ear-EEG devices in this work were easily wearable and very comfortably. These results suggest that ear-EEG is a promising alternative EEG-acquisition method that is more user-friendly and suitable for BCI system that aims for daily-life usage comparing to the conventional scalp-EEG method.