Ordinary smoke alarms will only do this one thing
Fire safety is important, and smoke detectors perform a critical part in keeping your family safe. Even so, smoke detectors have various shortcomings. For example, they will only identify smoke, not heat. If there is a fire in your home, you may not be alerted unless the smoke ascends to the smoke detector. While there are additional unmistakable indications of fire -- such as a sudden rise in heat -- if you don’t have smoke, there is no triggered smoke detector.
In addition, smoke detectors only activate when they encounter ample smoke. If a fire begins slowly, you may not be cautioned until the situation is out of hand. Various smoke detectors employ more than one sensor, which means they will detect smoke from both roaring flames and something less intense. Then when they sound their alarm, it's up to the occupant to notify the fire department after they safely leave the property.