A smoke detector is a safety device that helps protect homes and buildings from fire. It works by sensing smoke in the air, which can indicate a fire. When smoke is detected, the device emits a loud alarm to alert people nearby, giving them time to escape and call for help. There are different types of smoke detectors, including ionization and photoelectric models. Ionization smoke detectors are better at detecting fast-burning fires, while photoelectric smoke detectors are more effective for smoldering fires. It's important to regularly test and replace the batteries in these devices to ensure they work properly when needed.