Systems and methods related to the field of cardiac resuscitation, and in particular to devices for assisting rescuers in performing cardio-pulmonary resuscitation (CPR) are described herein. A method for providing Cardiopulmonary Resuscitation (CPR) treatment to a person in need of emergency assistance includes obtaining from an accelerometer positioned to move in coordination with a patient's breastbone values for depths of a plurality of the chest compressions, obtaining from a light sensor affixed to the patient information about light detection, and determining, based on the information from the light sensor, whether a rescuer is releasing the chest of a patient during manual CPR chest compressions.
