Just got a few of these (1 to power some warm lights which will heat my water-line's pressure switch), in order to keep my water from freezing at the pressure switch. I thought I'd mention here that these could be used to avoid losing plants to the cold within a greenhouse. I got the Ranco brand ETC 111000-000.
Basically, this thing powers an outlet whenever the temperature probe detects a temperature outside of the set range. This can be used the following way as 1 example:
Say that you have plants in a greenhouse that you are concerned may get too cold and perish; you can set the device's on-when-reaches-temperature & the off-when-reaches-temperature, then plug in a heater.
Ranco ETC 111000-000 - 120V Wiring Guide From Habanero Smoker [not my doing, but I like it]
3/8 inch Romex ConnectorDiagramClose up of DiagramI just now followed this guide and wired up one of these myself, and used a hair dryer to test it, and 2 glasses of water (1 hot; 1 cold). All I had to do was cut an extension cord in half and follow the easy guide to hook up the male & female plug-ins to the device.
P.S. This can be set to heat or cool, and the temperature differential can be set anywhere from 1 to 30 degrees; these can operate on 110 or 220 power.