Why Do Smoke Alarm Batteries Always Die At Night?

Would I be correct in assuming that prior to asking the question 'Why do smoke alarm batteries always die at night?' you might also have been experiencing a few 2am wake-up calls - that annoying “chirp … chirp”.

Some of us will lie there waiting, hoping it will shut up, while others have been known to tear the smoke alarm off the ceiling, while frantically trying to wrench out the battery in the dark. 

Why does it always occur in the middle of the night, and scare you half to death when it happens??

Answer

Step 1

Temperatures drop during the night. When you have a battery that is near the end of its life, it may produce just enough power during the warmth of the day to satisfy the detector. However, when the evening temperatures drop enough to slow the chemical reaction of the battery, and thus the electrical output, the detector warns that the battery is too weak to function. And that is why they almost always wake us up in the middle of the night!

Smoke alarm batteries are really not all that mysterious!

As you know, smoke detectors generally operate on batteries or have a backup battery. 

When these batteries fall below a certain voltage as they reach their “use by” date, the detector warns us by chirping. 

Electricity is produced by a chemical reaction inside the battery. 

As with most chemical reactions, lower temperatures cause these reactions to occur more slowly. 

This results in reduced electrical output, so the detector is simply telling you that the battery is almost dead.

As you are aware, temperatures drop during the night. 

When you have a battery that is near the end of its life, it may produce just enough power during the warmth of the day to satisfy the detector. 

However, when the evening temperatures drop enough to slow the chemical reaction of the battery, and thus the electrical output, the detector warns that the battery is too weak to function. 

And that is why they almost always wake us up in the middle of the night!

So why does it always seem to die at night?

Rest assured, there is a reason for this seemingly nonsensical occurrence. 

As touched on above, the 9-volt battery within the smoke alarm has a chemical reaction going on inside that produces a voltage, in this case 9-volts. 

When air temperatures are warm, for example, during the day, and it’s also warm up there on the ceiling, this aids a battery’s chemical reaction and keeps the voltage output at a level that the smoke alarm is happy with. 

As the temperature drops at night time, or with cooling air conditioning turned on, the battery’s chemical reaction slows and the voltage lowers. 

When the smoke alarm’s chirp sounds, the internal circuit of the smoke alarm has detected that the battery voltage is too low and must be replaced.

It’s not that the battery is just all of a sudden dead or dying. 

It’s actually been that way for a while but almost always, you’ll notice it during the coolest part of the day, which is usually at night time.  

I would add that this small resultant drop in battery voltage is only ever apparent in a suspect battery anyway (that is, one that is low on charge), so it wouldn’t be noticeable at all in a healthy battery.

Can you reduce the possibility of this happening?

So briefly, in conclusion, I would like to add that this phenomenon is not something you really need to worry about if you diligently carry out your annual battery changes. 


I hope you’ve benefited from this article and your questions have been answered. 

I’d love to hear any feedback you have in the Comment Box below. 

You might also like to share a story or two in relation to your experiences with nuisance and/or dying smoke detectors. 

Do you have any more questions? I’d be more than happy to help!


Luke Pritchard
Luke Pritchard

Luke is an electrician of 19 years and founder of 'Smoke Alarmed' - a smoke alarm installation, service and testing company on the Sunshine Coast, QLD Australia. Husband and father to two ‘hyperactive’ boys, and one little girl just as 'rough and tumble' - if he looks a little bruised and sleep-deprived, that’s probably why ;) 9th worst surfer on the Sunshine Coast.

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