21.   When setting clocks back, change batteries in smoke alarms and carbon monoxide detectors.

22.   You also should change the batteries.

23.   Safety officials suggest that this annual ritual is also a good time to change the battery in each smoke detector, to be sure they will work if needed.

24.   The batteries must be changed every four hours.

25.   The Consumer Product Safety Commission recommends that batteries be changed in smoke detectors when clocks are reset.