Ok, so it doesn't rhyme, but you get the idea. It is recommended that you change the battery in your smoke and Co2 detectors twice a year. An easy way to remember to do so is to change them in the spring and fall when you adjust your clocks for daylight savings. Tonight is the night we all need to wind those clocks back and gain an hour of sleep (or whatever frivolity you plan on doing tonight). So go buy new 9 volts and trade out the old ones. It's cheap and keeps your family safe.
Now if there were only a way to protect the family from leftover Halloween candy, Hmmmmm.