Damn Smoke Detector!

Why do smoke detectors have to chirp at the most inconvenient time? Early this morning at 3:45am or so it started off with a chirp. That woke me up but I don't think it woke Fiona up. I decided to ignore it hoping that it was just a warning and won't keep chirping. Five minutes later it did and then the frequency was getting shorter. Fiona was up by then and I had to just change it. That meant turning on the lights, finding a 9 volt battery (luckily we have one left) and I had to change it out. Since we've moved in 4 years ago, I have only changed out a smoke detector battery once. That first time it happened was also in the wee hours of the morning. I had no clue what to do because, at that point, I hadn't changed one out. I ended up setting it off and I was really freaking out because I didn't want to wake Fiona or Jadon up (plus I was groggy up to that time). I know, I know, I'm bad. I should be doing it at least once a year. Guess what I'll be doing after work?