The Semi-Automatic model analyses the patient's ECG and if a shockable rhythm is detected it automatically starts charging the reservoir capacitor. The AED vocal message will suggest the operator to press the shock button to deliver the defibrillating shock. The phase following the defibrillation, that is Cardiopulmonary Resuscitation, will be guided by voice prompts and the metronome marking the various cycles of compressions and insufflations.