Puffer thief

Puffer thief is a slang term used by a few police forces in the United States to denote a criminal who steals a vehicle left unattended by its driver. In these cases, the vehicle has been left unattended by the driver (and any passengers) for the purpose of warming it up on cold days while they keep warm inside a nearby building. The term "puffer" is coined from the often noisy engine warming up, and the billows of visible smoke it produces from the exhaust on cold days.

In the majority of areas (if not overwhelming majority), it is illegal to leave a car unattended with the engine running, even if the car is left in park. This may be one of those laws that is on the books, but in practicality, is never enforced. However, some people believe that the law has a purpose; there have been cases of drivers leaving vehicles in neutral instead of park, allowing the vehicle to roll on its own and strike other vehicles or other objects, even pedestrians.

Drivers are advised that, if they must warm their vehicles in this manner, to always be within close range of the vehicle, to keep it in sight, and that doing so in the "saftey in numbers" of a crowded parking lot is no guarantee of safety.