For those interested look up a 'Thermo Cube' on Amazon. It's $15 - $20 and depending on which model you buy turns on/off the power depending on the temp. Great for those only wanting to run their block heater when it gets cold (again you can pick different model for different temps for when it goes on/off). Here's the one that turns on power at 35 degree's:
LINK
I've used one for years as I have mostly outdoor dogs with heavy duty dog house (double insulated, heated, and A/C in summer - and big....so no worries if/when I'm in the dog house.
) so use it on their water container and a water heater in it for when it's going to freeze. You don't have to worry about it over heating the water during those weird days where things warm up, cause the power gets cut off by this device at 45 degrees. So it regulates.
Am sure there's other manufactures as well, but most in same price range. Save some $$ for the other cool stuff for our trucks!