From Reno Fire on importance on keeping bedroom doors closed. SOUTH LAKE TAHOE, Calif. - Time is of the essence when fire hits your home. Things can rapidly change from smoke to flames, sometimes giving those inside very little time to get outside to safety. Even though smoke detectors have been required in new construction and in homes undergoing a remodel for decades, not all homes have working detectors. They are broken, have a dead battery, or missing completely. Batteries in smoke detectors that require them should be changed twice a year. A good time to remember to check your smoke alarm and change the batteries is when you change your clocks twice a year as daylight savings time begins and ends.