A sleep monitoring device comprising: a housing shaped to fit the contours of a patient's face; at least one pair of photosensors positioned to detect blood volume in the face of the patient; at least one air-flow sensor positioned to detect airflow during breathing of the patient; a data storage disposed in the housing and configured to store physiological information related to the detected blood volume and store physiological information related to detected airflow during breathing; a controller disposed in the housing and configured to control the at least one pair of photosensors to detect blood volume, to control the at least one airflow sensor to detect airflow, and to control the memory to store physiological information related to the detected blood volume and store physiological information related to detected airflow during breathing, during a predefined monitoring period; and a processor configured to obtain plethysmography data related to the detected blood volume from the stored physiological information, wherein the processor is further configured to identify respiratory effort by: detecting changes in a DC component of the plethysmography data, detecting pulse waves in the plethysmography data, calculating a measure of changes in vascular tone for each detected pulse wave, adjusting dimension of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, scaling intensities of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, and subtracting the adjusted measure of the changes in vascular tone from the DC component of the plethysmography data to obtain the respiratory effort. a housing shaped to fit the contours of a patient's face; at least one pair of photosensors positioned to detect blood volume in the face of the patient; at least one air-flow sensor positioned to detect airflow during breathing of the patient; a data storage disposed in the housing and configured to store physiological information related to the detected blood volume and store physiological information related to detected airflow during breathing; a controller disposed in the housing and configured to control the at least one pair of photosensors to detect blood volume, to control the at least one airflow sensor to detect airflow, and to control the memory to store physiological information related to the detected blood volume and store physiological information related to detected airflow during breathing, during a predefined monitoring period; and a processor configured to obtain plethysmography data related to the detected blood volume from the stored physiological information, wherein the processor is further configured to identify respiratory effort by: detecting changes in a DC component of the plethysmography data, detecting pulse waves in the plethysmography data, calculating a measure of changes in vascular tone for each detected pulse wave, adjusting dimension of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, scaling intensities of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, and subtracting the adjusted measure of the changes in vascular tone from the DC component of the plethysmography data to obtain the respiratory effort. detecting changes in a DC component of the plethysmography data, detecting pulse waves in the plethysmography data, calculating a measure of changes in vascular tone for each detected pulse wave, adjusting dimension of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, scaling intensities of the measure of the changes in vascular tone to match the detected changes of the DC component of plethysmography data, and subtracting the adjusted measure of the changes in vascular tone from the DC component of the plethysmography data to obtain the respiratory effort.