An apparatus for monitoring health status of a user, comprising: a sensor adapted to generate sensor data; a memory adapted to store one or more baseline biological marker for the user determined by performing measurements of the user and analyzing historical sensor data for the user, wherein the one or more baseline biological marker is used as baseline and include a baseline respiratory rhythm marker; a processor coupled to the memory and the sensor, wherein the processor is adapted to: receive an estimate of activity level by a user input, operate on the sensor data and the estimate of activity level to generate the baseline, wherein the baseline further includes a baseline cardiac health measure, a baseline estimate of activity level, and one or more baseline validation factors referring to one or more items of data determined from the sensor data other than items of the sensor data used to determine the baseline cardiac health measure, use one or more baseline validation factors to validate the estimate of activity level to the baseline estimate of activity level, wherein the processor is further adapted to: in response to detecting that the user is performing physical activity, determine biological markers from the sensor data; analyzing covariance of one or more of the biological markers determined from the sensor data with respect to the corresponding baseline for the user; and provide a notification indicating a change in health status based on the analysis. a sensor adapted to generate sensor data; a memory adapted to store one or more baseline biological marker for the user determined by performing measurements of the user and analyzing historical sensor data for the user, wherein the one or more baseline biological marker is used as baseline and include a baseline respiratory rhythm marker; a processor coupled to the memory and the sensor, wherein the processor is adapted to: receive an estimate of activity level by a user input, operate on the sensor data and the estimate of activity level to generate the baseline, wherein the baseline further includes a baseline cardiac health measure, a baseline estimate of activity level, and one or more baseline validation factors referring to one or more items of data determined from the sensor data other than items of the sensor data used to determine the baseline cardiac health measure, use one or more baseline validation factors to validate the estimate of activity level to the baseline estimate of activity level, receive an estimate of activity level by a user input, operate on the sensor data and the estimate of activity level to generate the baseline, wherein the baseline further includes a baseline cardiac health measure, a baseline estimate of activity level, and one or more baseline validation factors referring to one or more items of data determined from the sensor data other than items of the sensor data used to determine the baseline cardiac health measure, use one or more baseline validation factors to validate the estimate of activity level to the baseline estimate of activity level, wherein the processor is further adapted to: in response to detecting that the user is performing physical activity, determine biological markers from the sensor data; analyzing covariance of one or more of the biological markers determined from the sensor data with respect to the corresponding baseline for the user; and in response to detecting that the user is performing physical activity, determine biological markers from the sensor data; analyzing covariance of one or more of the biological markers determined from the sensor data with respect to the corresponding baseline for the user; and provide a notification indicating a change in health status based on the analysis.