Method and continuously wearable noninvasive apparatus for automatically detecting a stroke's onset are invented. The method comprises measuring pulse transit time or a related hemodynamic parameter and using adaptive pattern learning and stroke identification algorithms to identify the start of a stroke attack. The algorithms are run on an embedded processor and electronics in the apparatus. The result of the identification and detection is used to generate an alarm to alert the patient, caregiver or medical professional to immediately seek further medical treatment. The method can also be applied to identify and detect other abnormal health conditions.