A fridge thermometer is a device used to monitor the internal temperature of a refrigerator and freezer, ensuring food stays at safe temperatures (around 3-5°C for the fridge, -18°C or below for the freezer) to prevent spoilage and bacterial growth. Available in analog (dial) and digital (LCD) types, they often have features like max/min memory, hooks, or magnetic backs for versatile placement, helping you maintain freshness and food safety.