My uncle past away a few years ago, and we got this simple devise from his estate. It works similarly to a light timer except it works off temperature, not time. When he would go down to Florida during the winter, he would plug this thing into the wall, then plug a spot light into it, aimed out the window to a trusted neighbor's house. I recall my uncle set his furnace to 60 degrees and the devise to 50 degrees. If the house temp went down to 50 degrees, the spot light would go on warning the neighbor to check his furnace.
You can plug whatever kind of warning you want into the thing....something that makes either noise or light. I would imagine you can buy these devices at most home improvement centers. The devise works off 110V, not 12V, but who knows, maybe some can be found working on 12V if that is what you need.
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