Review on AC Voltage Display: DROK 3pcs Digital LED Display Voltmeter for AC 60-500V Voltage Monitoring, 110v 220v Volt Detector with Green Red Yellow Signal Indicator Light Panel by Dustin Lannan

Like others here I installed these next to my circuit breaker to hook up my generator. In my photo, the green pressure gauge was used for the supply network and the red pressure gauge for the generator (does not work in the photo). I have set up a "lockout" scheme so that only one of the two power supplies in the house is running at any one time, but it helps to know when mains power is restored so the generator can be turned off (otherwise you'll have to go to your disturbing neighbors or looking at the lights on the street). Especially when compared to the cost of the rest of the generator installation project, these sensors are an inexpensive and practical addition.