AEDs that are available to the general public may be either fully automatic or semi-automatic. The fully automatic versions tend to have fewer buttons and are often activated as soon as it is opened Likewise, the fully automatic AEDs may allow users to produce a shock treatment with the push of one button, while others may perform this task automatically.

The AED user who uses the fully automatic version has no interaction with the device while in operation aside from following the key prompts and placing the shock pads.

Trained responders and other health care professionals may use semi-automatic devices. These defibrillation devices typically include an ECG display and readout, user override capabilities, and rhythm analysis software. Unlike the fully automatic version, the user must perform additional life-saving tasks in order for the defibrillation to be effective and accurate. On the other hand, the semi-automatic versions allow trained health care personnel to provide an exceptionally high level of patient care.

AEDs require very little training to use. The machine automatically diagnoses the patient's condition, determines the current versus desired heart rhythm, and determines whether or not shock is needed. Fully automatic versions will deliver the shock without any commands from the user. Semi-automatic versions, on the other hand, will tell the operator that shock is needed, however, the user must actively tell the defibrillator when to deliver the shock, usually by pushing a button.

Because some AED users may be hard of hearing, many now include visual instructions as well as voice prompts. The majority of these units are designed to be used by non-medical or untrained operators. They are easy to use, giving rise to the placement of public access defibrillation units (PADs), which are being placed in large public facilities such as airports.