The battery in your smoke detectors should be changed yearly usually in the fall around Daylight Savings Time. The newer detectors are a combination smoke & carbon monoxcide.detector.
A smoke detector should be replaced every 10 years. This should be made a priority as it is the first warning that there may be a potential fire. Please refer to your detector's owners manual for proper guidance.
Too many people are losing their lives in fires. As any fire investigator will tell you, I know that a lot of fire deaths and injuries can be avoided by following a few simple steps.