Here’s another reason to unplug your microwave when you’re not using it: You could start a fire if your microwave accidentally turns on when it's empty. A microwave uses a magnetron to create electromagnetic waves. It attacks the water molecules in food and creates a vibration, which creates heat and then cooks whatever you’re heating up. If there’s nothing inside the machine that can absorb the electromagnetic waves, they have nowhere to go but back to the magnetron, which can overheat and cause a fire. An unplugged microwave ensures it won’t accidentally turn on.