A system for assisting a rescuer in performing cardio-pulmonary resuscitation (CPR) on a patient includes: a proximity sensor configured to be positioned at a location corresponding to a location of a rescuer's hand when delivering compressions to a patient's chest, the proximity sensor configured to produce a signal indicative of the rescuer's hands being released from the patient's chest; a medical device operatively coupled with the proximity sensor and configured to provide resuscitative treatment to the patient; and a controller communicatively coupled with the medical device and the proximity sensor. The controller is configured to: determine, based upon the signal from the proximity sensor, if the rescuer's hands have been released from the patient's chest, and trigger an action by the medical device in response to a determination that the rescuer's hands have been released from the patient's chest.