A heated jacket works by using electric power to warm up thin heating elements sewn into the fabric. These elements are connected to a small battery pack that you can recharge, much like the battery in your smartphone. When you turn on the jacket, the electricity flows from the battery to the heating elements. The wires inside the jacket then warm up, and the heat spreads across your body. Most heated jackets have multiple heating zones, such as the chest, back, and sometimes the sleeves. You can control these zones individually in advanced models or switch the whole jacket on and off. Some jackets come with several heat levels, allowing you to select low, medium, or high heat depending on how cold it is outside.