The OMRON H7ET-NFV is a great little totalizing hour meter that I installed on my heat pump compressor main contact coil. The 21-22 VAC that energizes the coil does reliably trigger the counter even though it is slightly below the 24-240 VAC specs on the counter. The counter is easy to set up and is internally 'powered' with a CR2477 battery. The 1000mAh battery is supposed to last 7 years. The OMRON manual will not tell you that it is a CR2477 battery. You heard it here first.
I deducted a star because the counter will reset when you change the internal battery. I'm going to have to figure out a way to keep the unit powered with 3V while I change the battery so that my counter does not reset.