How to know when to change battery in smoke detector

Have you ever wondered how often should smoke alarm batteries be changed?

You have installed smoke alarms in your home for your safety in the event of a fire, right? 

Therefore, I’m sure you will agree that it’s essential to maintain them to make certain they always work the way they should to protect yourself and your family if ever there is a fire in your home. 

After all, they are an investment in a way, and proper maintenance of these devices could certainly prove to be lifesaving. 

Smoke alarms save lives but not if the battery is flat, plus a working smoke alarm will give you an early warning, and of course, time to escape a fire.

Answer

Regardless of what type of smoke alarm you have, whether it be a 9-volt battery powered alarm or a mains powered alarm with a 9-volt backup battery, if your smoke alarm has a removable battery, it should be replaced once per year. 

To answer the topic thoroughly and in more depth however, there are many more helpful facts I’d like to pass onto you. 

Please read on and you will discover a wealth of additional information, all related to smoke alarm batteries.

How Many Types of Smoke Alarms are There?

Firstly, let’s find out what type of smoke alarm you have, as this will determine how often you will need to change the battery. Here are the 4 types available:

9-volt battery powered (but not mains-powered) smoke alarm

#1

These alarms often won’t have a green light, which usually indicates the smoke alarm is mains powered. When you remove the body of the alarm from its base, it will contain a removable 9-volt battery. These are the most common smoke alarms seen in homes across Australia. These alarms require the battery to be replaced once per year.

10-year-life lithium battery powered (but not mains-powered) smoke alarm

#2

Again, these alarms often won’t have a green light (which usually indicates the smoke alarm is mains powered) and when you remove the body of the alarm from its base, unlike the alarm above, you won’t actually see a 9-volt battery. These alarms contain a sealed, non-removable 10-year-life lithium battery and as such won’t require any battery replacement for the life of the alarm, which is 10 years.

Mains powered smoke alarm with 9-volt backup battery

#3

These are the alarms where you’ll often see a permanently lit green light and when you detach the body of the alarm from its base, it will contain a removable 9-volt battery. This is the second most common alarm seen in homes across Australia. These alarms will require a back up battery to be replaced once per year.

Mains powered smoke alarm with non-removable 10-year-life lithium backup battery

#4

These are the alarms where you’ll often see a permanently lit green light and when you detach the body of the alarm from its base, you won’t actually see a 9-volt battery. These alarms contain a sealed, non-removable 10-year-life lithium battery and as such won’t require any battery replacement for the life of the alarm, which is 10 years.

How Will I Know if My Smoke Alarm Needs a New Battery?

Most smoke alarms will emit a small chirp/beep once every 30 to 60 seconds, and as annoying as it is, please don’t ignore it as this indicates the battery needs replacement. 

This chirp is a very different sound to that of an alarm (when you would hear the siren sound for longer). 

These low battery warning chirps will be quick, high pitched chirps heard continually every 30-60 seconds.

As a general rule of thumb, even for the best smoke alarms on the market, you should form the habit of testing them at least once a month. 

Press and hold the test button on the smoke detector. 

Press and hold the 'Test' button on your smoke alarm until you hear the siren sound

A broom handle will also work well for this test. 

It can take a few seconds to begin, but a loud, ear-piercing siren should emanate from the smoke detector while the button is being pressed. 

If the sound is weak or nonexistent, you need to replace your batteries. This is relevant for non-mains-powered alarms. If the sound is weak or nonexistent from your mains powered smoke alarm, the entire smoke alarm will require replacement.

 Remember, Mains Powered Smoke Alarms Need Their Batteries Replaced Too!

If yours is a mains powered smoke alarm with a replaceable 9-volt alkaline battery and the beeping/chirping coincides with the red LED indicator flashing (once every 40 seconds or so), then this is an indication that the back-up battery is in need of replacement.

A quick chirp heard from your smoke alarm once every 40-60 seconds coinciding with a red flash on the alarm, usually means the back up battery in your mains powered smoke alarm needs replacing.

A common misconception I hear is that owners of mains powered smoke alarms, (otherwise referred to as hard wired) don’t think they need to replace the batteries in their alarms. 

Their reasoning is that because their alarms are mains powered, they don’t have a battery at all. 

But all mains powered alarms still need a back up battery to power the alarm in case the power goes out. 

These back up batteries need replacing too. 

Back up batteries in mains powered alarms can either be a replaceable 9-volt version (these require replacing once per year) or there are some mains powered alarms that contain a 10-year-life rechargeable lithium backup battery.  

With this type of alarm, you don’t need to replace any batteries. 

Remember though, if you have mains powered alarms containing a 9-volt backup battery, adopt the same routine and replace these back up batteries like you would with the standard 9-volt battery powered alarms, which, of course, is once per year.

How to Replace Your Smoke Alarm Battery

I plan to cover this in more detail in a future guide. However, this condensed version should help for now if this is something you are wondering about. 

To access the battery compartment of your smoke alarm, you’ll first need to detach the body of the alarm from its base. 

Most smoke alarms in Australia will either unclip and hinge down, twist off in an anti-clockwise direction, or slide off the base in one direction (often with an arrow as a guide). Some may need a screwdriver inserted in a certain spot so it unclips and then slides.

To remove this smoke alarm, a screwdriver needs to be inserted in the side whilst the alarm is pushed away

To remove this smoke alarm, a button is pressed near the ceiling and the alarm hinges down

This type of smoke alarm slides off in the direction of the arrow seen on the face of the alarm

This type of smoke alarm twists off anti-clockwise to remove it

Read the instructions specific to your alarm which are generally embossed or clearly marked on the face or side of the alarm.

Then insert a brand new, fresh 9-volt battery in the battery compartment, paying attention to the positive and negative terminals indicating which way to insert the battery.

You might observe that some alarms have a plastic tab on the side of the battery chamber which needs to be folded in whilst you insert the battery.

Do not re-install the smoke alarm back on its base with the plastic tab sticking out

If your smoke alarm has a plastic tab adjacent to the battery chamber, fold it in whilst inserting the battery

Also ensure the battery terminals are free of corrosion. A small piece of sandpaper (emery paper) can often be used to clean the battery terminals if you find them to be dull or corroded.

Check for corrosion on the battery terminals

Reinstate the body of the smoke alarm onto its base in the reverse manner.

A tip is to write the installation date on the battery before you insert it so you have a clear record of exactly when it was installed.

TIP: Write the installation date on your smoke alarm battery prior to inserting it

What Is the Best Type of 9-Volt Battery to Install in My Smoke Alarms?

My recommendations would be:

Any Tips on How to Remember to Change My Smoke Alarm Batteries?

I can’t stress enough the importance of changing your smoke alarm batteries in a timely manner.  

Unfortunately, statistics show that most deaths which occur because of a house fire could have been prevented if the household had working smoke alarms. 

That is why it is so important for you to choose a mental trigger or other reliable reminder that will work for you when it comes time to change your smoke alarm batteries. 

Here are a couple of suggestions:

It doesn’t matter what mental trigger you adopt, just ensure it is automated, consistent, and doesn’t need regular manual input so it is not forgotten.

If you’re up with tech, the best way is to set a recurring annual reminder in your calendar system.

Hey, otherwise maybe just write it in big, bold wording on your paper calendar each year. It’s whatever works for you!

How Long Will Batteries Last in a Smoke Detector?

The short answer is generally at least a year, but usually not more than 2. 

We’ve actually seen a back up battery in a mains powered smoke alarm last 8 years, but on the flip side of the coin, we’ve seen them last just 6 months! 

There are a number of variable factors. Much of this will depend on the general and standby power consumption of the smoke alarm, the quality of the battery installed, the age of the battery installed and the temperature of the environment in which it is installed.

Will Smoke Alarms with Lithium Batteries Ever Need Replacing?

Yes, they do. 

If your smoke alarm uses a lithium battery, it is inbuilt into the alarm and cannot be replaced. The entire unit needs to be replaced every 10 years. 

The batteries in these alarms are designed to last the life of the smoke alarm, in which case the battery will have served its purpose after 10 years.

Most alarms which contain a 10-year-life lithium battery will have an in-built low battery warning like their 9-volt counterparts. 

This applies to both mains powered or stand alone lithium battery powered alarms. 

When the lithium battery is low, they too will emit a quick chirp once every 30-60 seconds. 

As mentioned above, these 10-year-life lithium batteries are supposed to last at least 10 years, which is long enough to service the 10-year life expectancy of the alarm. 

However, if you find your lithium battery powered smoke alarm is chirping before it has reached 10 years of age, it often indicates a battery failure. 

If this happens, contact the manufacturer of the smoke alarm and organise the replacement of the whole unit if it is still under warranty, or otherwise have it replaced by an electrician or smoke alarm professional.

10-Year-Lithium Battery Smoke Alarms are Trending

We are observing an increased trend in home owners choosing the 10-year-life lithium battery-powered smoke alarms, or mains powered alarms with 10-year-life lithium backup batteries. 

This indicates that people are now showing a definite preference for the 10-year lithium battery smoke alarms over the alarms which contain a removable 9-volt battery. 

As mentioned above, these lithium battery alarms do not require the 9-volt battery to be replaced in each alarm every year.

So why wouldn’t you consider them …? 

These smoke alarms are generally not much more expensive than the 9-volt battery models, and with the added benefit of saving 10 year’s worth of 9-volt batteries, plus your time and your sanity, these might be a justifiable investment and definitely worth considering if you are thinking about upgrading.

Can You Quieten a Smoke Alarm Which Has a Low Battery Warning (aka Chirping or Beeping)?

As discussed earlier, smoke alarms are designed to start beeping when the batteries are running low. 

This can cause your smoke alarm to make a chirping noise at times when smoke has not been detected. 

The fact that your alarm is beeping is a good sign – it means your device is still working well enough to detect the low battery power and let you know that a changeover is due.

Anyway, here are my 2 answers to the question:

Firstly, the best way of course, is to replace the 9-volt battery so it stops chirping … simple!

Secondly, some smoke alarms have a low battery warning ‘Hush’ feature. 

The way this usually works is that if your smoke alarm starts chirping once every 30-60 seconds when you don’t happen to have a new 9-volt battery on hand, some models allow you to press the ‘Hush’ button on the alarm (some may require a brief press and hold). 

This will silence the chirp for 24 hours, allowing you time to source and install a new battery. 

Not all smoke alarms are equipped with this feature. However, if you’re caught out one day, try pressing the ‘hush’ button once (or press and hold for a few seconds) as this may reset the low battery warning.

I’ve Replaced My Smoke Alarm Battery but it is Still Chirping? What Now?

I know, this is so frustrating when it happens! 

Give it time and have a little patience. Sometimes it may take a smoke alarm 15-20 minutes to reset and acknowledge a new battery has been installed, before resuming normal operation. 

More often than not however, a smoke alarm will stop chirping within a minute or two after you’ve replaced the battery.

Just make sure you’ve inserted the battery the correct way, paying attention to the battery polarity (that is, having the positive and negative terminals of the battery corresponding to the positive and negative tabs in the smoke alarm). 

If a battery has been inserted back to front, the smoke alarm won’t register a new battery has been installed. 

Who’d ever do that, you’re wondering! How easy is it though, in the middle of replacing a battery, to be distracted by a small child speaking to you, your puppy grabbing your socks off the floor and running off with them, or a breaking news story on TV for example! Or perhaps you're trying to replace the battery in the middle of the night and you're groggy and don't know which way is up! 

Putting a battery in back to front is very easy to do if you're not paying attention.

It might also be a good idea to check that there is no corrosion on the battery terminals. If there is, just use some fine sandpaper (emery paper) to give them a quick clean up.

If corrosion is found on the battery terminals, clean it off using some fine sand paper prior to inserting the new battery

Also, is the 9-volt battery you’ve inserted brand new or has it been stored in a cupboard for some time?  

Always aim to install a fresh battery where possible. 

It’s a good idea to inspect the shelf life/expiry date of the battery which is usually stamped on the side.

Maybe check the quality of the smoke alarm battery as well. Often the cheap ‘no-name brand’ batteries have poor lasting ability compared to the well-known quality brands, albeit with a much higher price tag, which will usually outperform their cheaper counterparts.

Another thing to be aware of … we’ve seen several instances of multiple faulty 9-volt batteries from the same packet. 

On the rare occasion that you’ve found yourself with a dud battery, don’t always assume another one in the same packet will be any better. 

To rule out any doubt, try a new, fresh battery from another packet or from a different place of purchase.

Over To You Now ...

I trust that you’ve enjoyed this article and have come away with a better understanding of some of the complexities of smoke alarm batteries plus the knowledge on how to best maintain your smoke alarms to keep them in peak working order. And hopefully I've been able to answer the question 'How often should smoke alarm batteries be changed?'

I’d like to give it over to you now as I’d value your feedback on this article. 

Did it help provide an answer you were looking for, or was there something I left out, and what did you find most helpful?

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.