Abstract: An AED includes defibrillation circuitry housed within an enclosure, a first processor programmed to periodically test the operability of the defibrillation circuitry and a second processor in communication with the first processor. The AED further includes a visual indicator, such as a red/green LED, positioned at the exterior of the enclosure that is operatively connected to the second processor. The second processor is programmed to control the visual indicator in response to the periodic test results provided to it by the first processor.