Power Oultage Alarm Perfect for Monitoring Refrigerators, Freezers, Sump Pumps, Aquariums Power Failure Alarm is MCU Monitors Voltage at All Times and Alarm Volume 95db Built-in Safety Lithium Battery 400mAh (CE certified),Continuous Alarm Time 8h Power Oultage Alarm with Mute Reset Button and With Switch Function and 15A Socket Plug in the 120V power supply, turn on the switch (ON position), the buzzer will prompt power on, the indicator light will be on, if you press the reset button, the buzzer will make sound for 2s. If there is a power failure (power supply voltage 30V), the buzzer will continue to sound, and the indicator light will be turned off. If the reset button is pressed, the buzzer will stop sounding. Until restart the device (button ON- OFF- ON). Power Failure Alarm is MCU Monitors Voltage at All Times and Alarm Volume 95db