Smoke detectors are meant to warn you of the presence of smoke in your home or office. The smoke could be coming from someone accidentally burning something they were cooking, an appliance overheating, a poorly ventilated active fireplace, or an open fire. The smoke detector acts as an early warning to help you act quickly so that you can remove yourself and your loved ones or colleagues away from the blaze.
The most common cause of death related to fires is smoke inhalation, not the flames themselves. This fact is what makes smoke alarms so important to the safety of any home or other building.