Depending on the type, AEDs can be semi-automatic or fully automatic. A semi-automatic defibrillator assesses the heart rhythm and if an abnormal heart rhythm requiring a shock is detected, the device prompts the user to click a button to deliver a defibrillating shock. They analyze heart rhythms and if an abnormal heart rhythm requiring a shock is detected, the device prompts the user to press a button to deliver a defibrillating shock. Fully automatic defibrillators assess the heart rhythm and deliver defibrillation shocks as directed by the device software. No user action is required.