What is the true evil? The CO detector or the Battery?

It happens every time. It is not before I go to bed that the battery starts the warning beeps. It is not after my alarm goes off in the morning that it will begin. NO, it is sometime in the middle of the night. It is when I am the most sound asleep. It is when the dogs are warm and cuddled up and (most importantly) peaceful beside me. It is when I am in the middle of an amazing dream. That is when the beeping starts. BEEP. And the first few times it happens, I am still in the middle of sleep, barely awake and unable to pinpoint what the problem is. BEEP. A little curious as to why I am awake, but have no idea what it could have been. Back to sleep. BEEP. One eye opens, easily fall back asleep, even catch a few remnants of the same dream. BEEP. Both eyes open now, but still no real worries, sleep again... BEEP. Now the dogs have begun to stir. I turn over, my arm goes over my ear and sleep... beep. (this time a little more muffled, but the arm is not completely working, besides that does not prevent the dogs from noticing). Miriam raises her head and looks at me like, aren't you going to do something about this? Seriously, that is the look she gave me. So I turn over look at the corner and wait... BEEP. But which is it, I still have no clue--the CO detector or the smoke alarm? BEEP. It is getting more persistent and more demanding now... BEEP. Okay, I am getting up. I throw the covers off. Burrrrrrrr. The windows are open and out of the covers is cold, so very cold. BEEP. Dragging the piano bench over now. Still don't know which one it is. BEEP. I think I know the who the culprit is. I remove the Smoke alarm and shove it under the sofa cushions to be dealt with later. All seems quiet. I crawl back in bed, oh how warm. Dogs get to resettle in their warm places. Ready for a little more sleep before facing the day... BEEEEEPPPPP. I chose poorly. It was not the smoke alarm, it was the CO detector. Back out into the cold, back up onto the piano bench (balance please), CO detector down, and it is now resting beside the Smoke alarm under the sofa cushions, back to bed, dogs back by my side. Sleep, Dream. ALARM CLOCK...