Most people use oil on squeaky door locks, but locksmiths actually prefer dry graphite powder because wet oils attract dust and dirt that eventually gum up the tiny pins inside the lock mechanism. The graphite works by leaving microscopic flakes between the metal surfaces that slide over each other like a deck of cards, reducing friction without the stickiness of oil. In freezing weather, oil-based lock lubricants can thicken and make keys nearly impossible to turn, while graphite powder continues working smoothly down to -40°C. A single puff of graphite into a keyhole can keep a lock working smoothly for years, whereas oil might need reapplication every few months as it collects grime.