Car thefts are on the rise thanks to the season's sharp frosts.
AA Autowindshields is warning thieves are on the look out for unattended cars being defrosted with the engine left running.
Research for AA AutoWindshields has shown that two-fifths (40 per cent) of drivers let their car's engine clear icy screens before they drive off.
But they are at serious risk of losing their car if they pop back indoors and leave the engine running, even for a moment.
Dean Hill, AA AutoWindshields' technician of the year, said: "To car thieves, frosty mornings are a Christmas gift.
"Keys are the weakest link in the car security chain and organised criminals are known to cruise suburbs looking for the telltale plume of steam rising from an exhaust and if the car is unattended, it takes only a few seconds for it to vanish.
"Unfortunately, car owners will also get a cold reception from their insurance company as loss by leaving keys in an unattended vehicle is specifically excluded from motor insurance policies."
An AA/Populus study of more than 22,700 AA members also found that although two-thirds (66 per cent) of drivers also use a scraper and 45 per cent de-icer, or a combination of both, 12 per cent admit that they don't bother to fully clear the ice off.
Young drivers (aged 18-24) are least likely to completely defrost the glass, a fifth (20 per cent) admitting they drive away with some or most of their car's windows still opaque with frost, dangerously reducing all-round visibility.
Another 13 per cent of drivers say they use hot water to clear ice: Women being more likely to do so (15 per cent) than men (12 per cent).
"Sudden expansion caused by hot water followed by contraction as it cools can cause the glass to crack, especially if it already has chips or small cracks," said Hill.
"On very cold days this method is ineffective, as the hot water will rapidly cool and almost instantly turn to ice."