Smoke detector batteries - it's something we hardly ever think about until the low battery "chirp" or, God forbid, an actual fire!
Today's building code requires smoke detectors to be "hardwired" to your electrical system. However, batteries are still required as a back-up in the case of a power failure.
If your smoke detectors are like mine, they only "chirp" to indicate a need for battery replacement in the middle of the night while you're in a dead sleep! I have actually considered using a broom handle to knock it off the ceiling because I couldn't reach it with a ladder. Ok, maybe anger management should be in my future...ha ha.
Anyway, annually replacing your smoke detector batteries will save you aggravation and/or possibly your life. (A good rule to follow is to link the date of the battery change to another special date e.g. Daylight Savings Time, New Year's Day, your birthday or anniversary, etc)
Today's code also requires smoke & carbon monoxide detectors. There is much debate as to the effectiveness of a carbon monoxide detector on the ceiling since the odorless gas is about the same density as air, by the time it builds up to the ceiling it may be at a toxic level that can kill.
There have been recommendations to install the carbon monoxide detectors a few feet above the floor, but the experts are still debating which installation is best.