Sleep is very important to keep our physical condition healthy. Many studies have been devoted to clarify the mechanism of sleep and to monitor the sleep all night. In this study, we paid attention to heart activity during sleep and have developed a nonrestraint monitoring method of heart activity using an acceleration sensor set inside the coverlet. This method is easy for the use of sleep monitoring at home in daily life. An acceleration sensor was set inside the coverlet as it opposing to subject's left chest. Subjects were asked to lie in supine position and the coverlet with an acceleration sensor was put on the subject. Mechanical vibration from heart activity expected to be carried to the acceleration sensor through the coverlet. As a result, periodic vibration was measured successfully and this vibration was proved to be in high correlation with the R wave of ECG in six subjects. The same results were obtained even in case of lying in right and left lateral decubitus position.
