You should replace you smoke detector batteries once a year at least and/or follow your manufacturer's instructions for replacement. Usually, in the spring or fall when we set our clocks back, we remind you to change your batteries. October is Fire Prevention Month, and this is also a reminder to change your batteries in the fall. You should test your smoke detector once a month to make sure it is working properly. If your detector is set off constantly by cooking, it will wear out the batteries sooner and you will need to replace them sooner. A chirping sound or constant beep usually indicates low batteries, but models differ from one another. The bottom line is that you have one and change the battery at least once a year. More information can be found at the U.S. Consumer Product Safety Commission.