Carbon monoxide and smoke detector batteries need to be changed at least twice a year, and this Sunday would be a good time. Knoxville Fire Department captain Barry Reynolds says daylight saving time ends this Sunday at 2 a.m., and as Marion County residents set their clocks back one hour, they should change their smoke detector and CO2 batteries. He says it’s important to get in the habit of changing the batteries twice a year during the beginning and end of daylight saving time.