My setup has a auto changeover valve with a red/green indicator to show empty or not. When one tank goes empty the level indicator turns red and the valve automatically switches over to the full tank. I periodically check the tank indicator to see if it's red. If I see it's red then I turn the valve lever towards the full tank, turn off the empty tank, have it filled, re-install and turn it on.
My appliances never run out of propane unless by some fluke I run both tanks empty before getting a fill.