Why is that smoke alarm batteries always seem to die at night and start beeping at 2am when you least want it to? To be clear, we’re talking specifically about a brief beep, followed by a pause, and another beep, and so on, that alerts you to the fact that the battery is dead and needs to be replaced.
Is it just an amazing, cruel coincidence that the chirping of your smoke detector occurs in the middle of the night? It turns out there is a scientific reason that this may be occurring…
As the temperature drops at night, a 9 volt or two AA batteries used in a smoke detector has more trouble producing the desired current than during the day when the temperature is higher. A battery is more susceptible to chirping at night as it gets close to needing to be replaced as a result.
Why does my smoke detector always seem to chirp at night when the battery dies?
Batteries – including small 9 volt and AA batteries used in smoke detectors – are particularly susceptible to a drop in temperature as they get older and need to be replaced. As the temperature drops, the chemical reaction in the battery slows and the transfer of the current to the device it is powering slows down as well.
At some point, your smoke detector is alerted to the lack of current and it begins to chirp to let you know it is not receiving enough power. In other words, the battery needs to be replaced.
But when the temperature begins to increase as night turns to day, it’s possible that the chemical reaction speeds up again and enough power is once again delivered to the smoke detector and the chirping stops.
People often turn down the temperature on their thermostat at night. This is combined with the colder weather outside the house when the sun has set particularly in autumn and winter.
This is why your smoke detector may start chirping at night but then stops in the morning when you wake up as the sun comes up and the heater kicks in and raises the in house temperature.
The coldest time of the day might surprise you…
The coldest time of the day occurs shortly after sunrise when the sun is still rising. At this point, the sun’s ray aren’t yet strong enough to counter the energy that is leaving the surface of the earth.
So if sunrise occurs around 6am, the previous several hours – let’s say 2am onwards – are also very cold and increasingly so as time goes on before the sun rises enough to counteract and reverse the cooling that occurred overnight.
Inside your home as the temperature also cools, it may take several hours for the inhouse temperature to drop low enough to trigger the smoke detector to alert you to a weakened battery that is close to replacement.
It’s during this time period that a weakened smoke detector battery may be susceptible to chirping when it is close to needing replacement.
How does temperature affect the output of small batteries?
As the surrounding temperature decreases, batteries have more difficulty delivering the required level of power, more so as the batteries age and reach their end of life.
Just like your car battery needs more time to turn over in cold weather, a small 9 volt battery or two AA batteries that you use in your smoke detector have trouble providing the necessary power as the ambient (room) temperature drops, and as the battery ages.
Your smoke detector has the ability to notice when the battery is dying and is having trouble supplying the necessary current to power the device. When this happens, your detector will let you know by chirping – beeping one time repeatedly – off and on until you replace the battery or the battery dies.
Don’t let the battery die. When it starts chirping, replace the battery as soon as you can.
When should you replace smoke detector batteries?
Authorities such as the National Fire Protection Association (NFPA) suggest replacing the batteries in your smoke detector every 6 months to be safe. Replacing batteries once every day on a milestone date you can easily remember such as New Year’s Day (January 1) or April Fool’s Day (April 1) is another option.
Some newer smoke detectors come with a built in lithum battery that is designed to last 10 years. So not only does the smoke detector presumably last that long, the battery does as well, meaning you never have to change it.
Why does my smoke detector battery keep dying?
If you recently changed your smoke detector battery but it starts chirping again and you need to replace it quickly, there are a few reasons why this might occur:
- The battery/batteries might have been faulty. I’ve seen this many times. You use some old batteries lying around your home – even new, unused ones – and they quickly die. It happens.
- The smoke detector is past its due date and needs to be replaced. Check the expiry date stamped on the model you bought as you might need a replacement.
- If your smoke detector recently got triggered and beeped for an extended time(s), it will drain the battery quicker than you’d like.
- If you have a hard-wired smoke detector with a battery back up, a malfunction to the power supply can cause the detector to run strictly off the battery which can kill it in about one month or less.
Summary
While a smoke detector battery can die at any time, it often seems that the detector starts chirping in the middle of the night when the battery needs to be replaced and there is a legitimate reason why. At night when the temperature in the home typically drops, a weakened (old) battery has more difficulty supplying the necessary power to a smoke detector which can trigger the low battery warning.
Then again, it might also be a simple coincidence that your smoke detector started chirping overnight because it has simply reached the end of its lifespan and needs to be replaced and it just happened to occur then.
Replace the battery as soon as possible but also double check the expiry date of your smoke detector to ensure that it hasn’t reached its end of life, too. In the future, you might decide to change all detector batteries in your house on the same day each year to be safe.