Abstract: Examples of systems, apparatuses, and methods for determining whether CPR is being conducted based on an impedance signal are described. An example system may include a defibrillator including a cardiopulmonary resuscitation (CPR) analyzer configured to detect an impedance signal between electrodes applied to a chest of a patient. The CPR analyzer may be further configured to transform the impedance signal to a frequency domain representation to provide transformed frequency data, and to detect peaks within the transformed frequency data. The CPR analyzer may be further configured to classify the impedance signal as one of CPR or no CPR based on the detected peaks. The CPR analyzer may be further configured to determine a chest compression rate based on the detected peaks.