Most fire related deaths occur at night, commonly from the ignition of smoldering smoking materials in sofas and mattresses, and also from cooking left unattended on the stove.
Modern materials and building construction mean that fires burn hotter and move faster than they used to. The temperature in a room can reach 800 degrees Fahrenheit within just a few minutes, and fire doesn't behave the way it's portrayed on TV. It's fast, it's hot, it's dark, it's disorienting. There is usually a very short period of time to get up and safely exit the building.
The presence of smoke alarms in these situations can literally make the difference between life and death for you and the ones you love. Test regularly and change the batteries every spring and fall.