What's the difference between an automatic & a semi-automatic Defibrillator?

Semi-automatic defibrillators will ask the rescuer to press a button to deliver a shock if needed and when prompted. Fully automatic defibrillators, on the other hand, automate this process and will deliver the shock automatically if needed. And it will tell the rescuer a shock is about to be delivered so that they can make sure they aren't touching the casualty.