What device is specifically designed to extinguish fires?

The fire extinguisher is a device specifically designed for the purpose of extinguishing or controlling small fires. It contains an extinguishing agent, such as water, foam, dry powder, or CO2, which can be deployed directly on the fire to smother it or cool it down, reducing its heat and preventing the fire from spreading. Fire extinguishers come in various types, each suitable for different categories of fires, ensuring that users can effectively respond to a fire incident safely and swiftly.

In contrast, the other options serve different functions: a fire alarm is designed to detect smoke or fire and alert occupants of a building, allowing for timely evacuation. A smoke detector similarly serves to sense the presence of smoke, providing early warning of potential fire hazards but does not extinguish fires. A water hose can be used to douse larger fires, but it is not specifically categorized as a fire-extinguishing device like a fire extinguisher, which is portable and intended for immediate use in emergencies. Thus, the fire extinguisher is the correct answer as it is engineered explicitly for the task of extinguishing fires.