This wearable sensor is intended as a "drowsiness detection system" that detects signs of unaware drowsiness based on the pulse waves measured from the driver's earlobe and provides sound or vibration notification. Maintaining a firm image that projects reliability and progressiveness, it incorporates a shape that fits the body with a soft body-contacting portion. As a precursor to products that protect lives and society by ensuring safe and secure travel for drivers and passengers and preventing stoppage of distribution due to accidents, its appealing and eye-catching design is universality-oriented, not eccentric.