I hope I'm not repeating myself from earlier in the thread! There is a weird thing right in my own dining room.
It says it's a humidistat. It's on the wall next to the thermostat, so at one time it was either active or was intended to be used.
There is no whole-house humidifier. There is no duct work for there to BE a humidifier! The heat in the house is baseboard electric heaters, which of course don't need ductwork. There is no place in the house where there used to be ducts, or a big humidifier. So why is there a control for one hanging on my dining room wall?