The present invention relates to a wearable device for healthcare and method for using the device. More specifically, the wearable device is worn on a finger for measuring the health data of the user, selected from one or more of heart rate, blood oxygen saturation, heart rate variability. Based on the measured data, the sleep quality can be monitored and recorded. Disorders such as obstructive sleep apnea (OSA), can be detected. The wearable device may include an optical sensor coupled with or embedded in a main body including a visible light emitter, an IR light emitter and a light detector being arranged along a longitudinal direction of the finger. During operation of the wearable device, the heart rate is monitored based on a detected light signal. When the heart rate is higher than an adaptive threshold, both heart rate and blood oxygen saturation are monitored.
