Not all AEDs are the same. In general however they do have common features such as : voice prompts, heart rhythm analysis, and internal memory.
Voice prompts: the AED guides the user during the resuscitation attempt by means of voice prompts and, in most devices, by written messages on a screen. Examples of voice prompts are: stand clear? do not touch the patient? analyzing rhythm? charging press to shock? start CPR? Voice prompts are usually available in different languages.
Heart rhythm analysis: AED will analyze the heart rhythm and learn if the victim is in cardiac arrest and decide whether or not a shock is required. The Cardiac Science range of AEDs can automatically detect Ventricular Fibrillation (VF) with a 100% sensitivity and 99.4% specificity. This means there is no risk of delivering a shock to victims that do not need one
ECG display: some AEDs have the ability to display the ECG, but this is not necessary for the non-medical rescuer. The ECG display only allows trained rescuers to monitor the heart rhythm during and after resuscitation.
Internal memory: AED incorporates a data collection and storage system. They can store event information such as timestamp, the ECG tracing, the buttons use log, amount of energy delivered, etc. The memory should be downloaded or printed out after each use of AED. This information is useful for further victim management after successful resuscitation and it allows medical supervisor to evaluate the AED program.