Monitoring patients' position is important, but there have been few studies related to validation. The objective of this study was to assess the validity of position monitoring measured using a wearable device by comparing the device's measurements to a patient's actual position. We constructed a wearable device with a three-axis gyroscope and applied it to 10 patients who were unable to change their position independently. We compared the actual angle of the position and the angle transmitted from the wearable device using a Bland-Altman plot and a receiver operating characteristic curve. We compared the actual angle of the position and the angle transmitted from the wearable device using a Bland-Altman plot, but it was difficult to observe statistical similarity. The angles transmitted from the wearable device in the lateral and supine positions showed significant differences. The cutoff value separating the lateral and supine positions was found to be 27.1∘ (sensitivity = 100%, specificity = 99.9%). Through our method, the measured values from the gyroscope-based wearable device did not accurately reflect the patient's actual position. However, the wearable device was able to distinguish the lateral position from the supine position.