DROK 90538 Flat Plug AC 80-300V Voltage Panel Power Line Volt Test Monitor Gauge Meter AC 110V 220V Digital LCD Voltmeter Doubles as a Voltage meter and as a Night light, great for immediate check on power health of devices Connecting to the switch plug directly or any other kind of switch plug, simple and easy to use DROK Voltmeter LCD display with Blue backlight, easy for you to view even in Dim light. There is potentiometer inside the meter for accuracy adjustment