You can't start it in gear - well unless you're very silly anyway! You have to active the intellistart before you leave the car. (one with a manual box anyway) Part of this activation makes you check whether the car is in gear or not.
I used to have a Clifford Avant Guard in a Punto auto. Was very sweet on those cold mornings. I used to turn the heater up full and on full whack before I left the car. Then, when it was cold in the mornings I used to start it up from inside when I was having my breakfast, 10 mins later it was all sweet and toasty warm for when I wanted to leave.