We see it every year. An increase in car thefts, when there is a decrease in the temperature. Car thieves are very savvy and know that we all hate being cold. They also know that often times, in an attempt to make ourselves more comfortable, we are willing to make their life easier by starting our vehicles and letting them warm up.
A running vehicle in a driveway is easily spotted by those wishing to steal it. The best practice would be to not start your vehicle until you are in it. However; I am aware that for some, that is not an option. In such a case I would suggest only warming your vehicle when you are able to keep visual contact with it. Lock the doors and keep a spare with you (this may hinder thieves long enough for you to call police) and use a theft deterrent device such as a steering wheel lock bar.
Please remember there is a new anti-idling ordinance and it should be observed whenever letting a vehicle idle. There are weather exceptions but they must be adhered to.