Drivers are being warned not to leave their vehicles unattended with the keys in and engine running to defrost windscreens after a number of thefts.
Three cars were stolen in Leeds over a two-day period after the owners left them unattended to warm up.
West Yorkshire Police said the "frost jacking" incidents had happened on 19 and 20 December.
Det Insp Dan Greenwood said leaving vehicles unattended in such a way was an "open invitation" to thieves.
Mr Greenwood said: "Either stay in your car while it warms up or use a scraper and de-icer to make sure your view is clear before setting off."