We use this oneIt monitors our sump pump, power loss, and temperature. We programmed it to call both of our cell phones. The funny thing is, we forget all about it, then when we get a call from our home number, we can't figure out what's going on, and hang up before the recording starts playing. :)
I don't think we've ever had a call for the temperature, but the other two functions work for sure.
Another thing we've done at a relative's house is plug a temperature controlled switch into an outlet by the kitchen window, and plug a clamp lamp into it. Clamped the lamp where it shines in plain sight of the window. When the house drops below the setting, the light comes on. Neighbor keeps an eye on it. I tried to find a link to what we used, but our internet is barely working at the moment. (Hope this post makes it through.)