I wonder how many people reading this can remember a time when someone mistakenly shut off the furnace switch in their home. I have a pet peeve when it comes to this common mistake. Years ago as I recall, the furnace switch always had a red cover and was labelled FURNACE EMERGENCY ON/OFF. Furthermore the switch was always located in the stairwell high up on the wall where it was very unlikely someone would mistake it for a light switch.
Today these switches appear in various places but mostly on the ceiling directly in front of the furnace. There are a couple of problems with this location that come to mind. First of all I usually need to get a broom or jump up to flip the switch for testing purposes. Secondly the location of the switch in the furnace room is a poor choice if there is a furnace emergency such as a gas leak or fire. I for one will not be running into a fire to try to reach the shut off switch.
The most annoying problem of course is if the unlabeled switch on the wall that is frequently mistaken for a light switch. When this happens the furnace will not run and all kinds of problems can arise. As many of you will know this is a mistake that can cost thousands of dollars if it is not caught soon enough. The fallout of this mistake can be frozen water lines and flooding.
I recommend installing a temperature alarm that can notify the homeowner if the temperature drops below a set temperature. There are less technical means as well such as using a sharpie marker to label the switch or buy the proper plate cover. I have also seen a piece of tape over the switch as well.