A self-heating can is a can that warms its own contents using two separated chemicals stored in its outer wall; breaking the barrier between them starts an exothermic reaction that heats the food inside. The user typically presses a button or inverts the can to mix the chemicals, often calcium oxide and water, waits a few minutes, and opens a hot meal with no stove or microwave. The technology suits the military, emergency kits, and outdoor pursuits, though the cans are heavier, bulkier, and pricier than ordinary ones, and the heating is gentler than a hob. Food safety is unchanged: the contents are commercially sterile before heating, and the chemicals never contact the food.