Last winter was the longest/coldest one we've had in over 30 years. With my cars parked in an unheated attached garage, I experimented with something different. I put one of these on the front seat floor:
http://www.laskoproducts.com/oscillating-ceramic-heater-model-5409/
and passed an extension cord into the car and plugged it in...usually about 3-4 hours before I intended to depart. Worked pretty well. Got the interior of the car toasty warm no matter how cold it was and cleared the glass of any leftover ice/snow and most of the car too. Had to remember to disconnect it before driving away, but that's a minor point. Heats the dash real well...maybe helps the door locks too. No downside yet.
http://www.laskoproducts.com/oscillating-ceramic-heater-model-5409/
and passed an extension cord into the car and plugged it in...usually about 3-4 hours before I intended to depart. Worked pretty well. Got the interior of the car toasty warm no matter how cold it was and cleared the glass of any leftover ice/snow and most of the car too. Had to remember to disconnect it before driving away, but that's a minor point. Heats the dash real well...maybe helps the door locks too. No downside yet.