Put the peanuts into a large crock pot and add the cajun seasoning, salt, garlic granules, and red pepper flakes. Stir to distribute the spices.
Bring a pot of water or a tea kettle to boil. Pour boiling water over the peanuts and cover by at least one inch. Stir again. Now add the liquid smoke and stir again. Turn the crock pot on high and cook for 8 hours stirring after the first 4 hours.
Using a slotted spoon, scoop out the peanuts into a colander to drain. Dry lightly with a dish towel and serve.