When the time falls back this weekend, your clock should not be the only household item that requires you attention. Firefighters say you should change the batteries in your smoke alarm detectors. A federal survey finds about 90% of U.S. households have smoke alarms but about 20%of them, do not have alarms that work. Each year, about 2,800 people die in house fires. Firefighters say if you have a carbon monoxide detector, you should also change the batteries on those as well.