I am working on a device that will spray a small amount of liquid (mist) and I need this thing to be work through our cold winters unattended. The device will have a small pressurized containing for the liquid (perhaps the size of a 12 oz soda can). I am looking for recommendations to keep the liquid from freezing during very low temps. I anticipate that the device will have a solar cell to charge a lithium battery. So, the solution would have to be a rather low power solution and it would also need to provide enough heat to the Arduino to keep it functional. It does not have to be worm, it just can't freeze.