We are headed for a global catastrophe. We've got chemical hand warmers and we have electronic as well. In various forms and yes you can even use a flashlight. So let's go back to this. The liquid fuel hand warmer, this one, will run for about 12 hours on about 25 milliliters of naphtha. The estimated fuel consumption of an idling engine is about 0.6 liters per hour of engine displacement. So this means that an idling 3.5 liter engine consumes about the same amount of fuel in 45 seconds as your hand warmer here does in 12 hours. So you want to grab a coffee or a quick meal. When the drive-through line is too long, consider heading to the takeout counter at 10 watts. This way you won't let your engine idle for more than 45 seconds.