When power is disrupted the strobe will begin flashing rapidly and intensely as the alarm sounds in conjunction alerting you that power has been cut off. The light produces a strong burst of intense light and sound. The unit will produce its strobe/alarm combination signal until power is restored or until the toggle switch installed on the front of the unit is turned to the off position. The source of the intense bursts of light is a xenon strobe that is easily accessed by unscrewing the lens. Replacement bulbs are available if needed but the bulbs are good for at least 3 years. Know when power is disrupted to vital electronic devices. Multiple color options available.