[NEXT "Story Continued Here..."] It can also kill you if you drowse while running the engine. Carbon monoxide produced by exhaust (also by incomplete combustion from flame-fueled devices such as propane and gas heaters) is a colorless, odorless assassin that's been responsible for at least two hunter deaths in Montana during recent years. It's safer to shiver a little inside a sleeping bag or, in lieu of one, to wrap yourself in newspapers, floor mats, and carpeting. Seat stuffing can also provide insulation in an emergency. If you have no other means of staying warm besides the heater, turn the car into the wind if possible, make certain the tailpipe is free of snow, crack a window on both the upwind and downwind sides, and run it only for five minutes every half hour. Be aware that intermittent engine use allows snow that has blown into the engine compartment to melt and refreeze on the wires, possibly impairing operation later. Never fall asleep with the engine running. An emergency toilet paper heater (see the instructions in "The TP Car Heater" on page 41) is excellent for emergencies. Don't laugh. I once used a roll to warm up the truck camper in the Missouri Breaks country during an antelope hunt when roads were caked with gumbo-and after three days still had plenty left for the conventional function.