Is it on or off as standard when you turn the key? I had to take the wife out at 4.30am and the roads were white. Thick frost kind of white. The car was all over the place and must be the worst car I have ever driven on frost. Now, I am presuming the light on the button I press means on but could it come on when the car reaches a certain temperature and if so is it possible to switch it off again. I would rather have control than a computer I would never trust.