Apparatus and methods are described including a mechanical sensor configured to detect a physiological signal of a subject. A control unit receives the signal over a time duration of at least two hours at a given period of a first baseline day, and determines a baseline physiological parameter of the subject in response thereto. The control unit receives the signal over a time duration of at least two hours at a given period of a second day, the period on the second day overlapping with the period over which the signal is detected on the first baseline day. The control unit determines a physiological parameter of the subject based upon the detected signal on the second day, and compares the parameter to the subjects baseline physiological parameter. The control unit generates an alert in response to the comparison. Other applications are also described.
