Hi...Yes, that is true and I also use a tire gauge.
Just in case you may not be aware, this system is NOT for setting tire pressure. It is a warning system for air leaks, low pressure, or blowouts. The coaches RV tires aside, pulling a tow car that blows a rear tire you may not know it right away and pull it like that. Most A class rigs you can hardly tell you are towing to begin with.
So it is a safety item for I would want to know if even my coach tires are for some reason dropping in pressure while traveling.