How often should you change smoke alarm batteries?
Updated
Short answer
Replace the batteries once a year, or twice if you tie it to the clock change. Do every alarm in the house on the same day, whether or not they've started chirping, so you're not changing one at a time at midnight. Sealed alarms with a built-in 10 year battery are the exception: their battery can't be changed, and the whole alarm is replaced when it chirps or reaches its date. The job takes 10 to 20 minutes and $5 to $20 in batteries.
Why it matters
The battery is the alarm's only power in a battery-only unit, and its backup in a hardwired one when the power goes out, which is exactly when fires from candles and generators go up. A battery runs down on its own schedule, not yours, and the alarm's answer to a low battery is a chirp. The chirp comes at night, because that's when the house is coolest and the battery's voltage dips, and the common response to a middle-of-the-night chirp is to pull the battery out and go back to bed. That's an alarm with no power, often for months.
Changing every battery on a fixed day, once a year or twice with the clocks, means the batteries are fresh before any of them can chirp. It costs a few dollars and removes the one failure that's entirely in your hands.
When to do it more often
The schedule has one modifier, and it goes the other way: sealed alarms with a built-in 10 year battery need no battery changes at all. If your alarms have no battery door, they're sealed, and the whole unit is replaced at the end of its life.
For alarms that do take batteries, change them sooner if one chirps between changes, if an alarm has sounded for a long stretch, which drains the battery, or if the batteries you used were a cheap brand you don't trust to last the year. Tying the change to the spring and fall clock change gives you twice a year and a reminder you can't forget.
What you need
- A step stool
- Fresh batteries of the type each alarm takes, usually a 9-volt or a pair of AA, checked against the old ones before you climb the stool
Steps at a glance
- Buy enough batteries for every alarm in the house, in the right sizes, before you start.
- Twist or unclip the first alarm from its mounting plate, or open its battery door.
- Take out the old battery and put in the new one, matching the terminals.
- Close the door or twist the alarm back onto its plate.
- Press the test button and hold it until the alarm sounds at full volume.
- Repeat for every alarm, and write the date on a piece of tape on the last one you do.
You're done when every alarm has a new battery and has sounded on its test button.
Signs it's overdue
- Chirping every minute or so, which is the low battery warning.
- A low battery message or light on an alarm or a smart alarm's app.
- An alarm that fails its monthly test, or sounds weak.
DIY or pro
This is an easy job, and there's no service that does it. Anyone who can stand on a step stool can do it. The only thing to get right is buying the correct battery for each alarm, since some take a 9-volt and others take AA cells, and a house may have both.
An alarm that still chirps with a fresh battery has reached the end of its life and needs replacing, which is a separate job and the one place an electrician might come in, for hardwired units.
FAQ
Why does my smoke alarm chirp after I changed the battery?
The alarm may need a moment to reset, so press the test button. If it keeps chirping, the alarm itself is worn out and needs replacing, not another battery.
Do hardwired smoke alarms need batteries?
Yes. The battery is the backup for a power outage, and it runs down and chirps like any other. Change it on the same schedule.
What battery does a smoke alarm use?
Usually a 9-volt or a pair of AA cells. Open the battery door and look before buying, since the alarms in a single house can differ.
Can I take the battery out to stop the chirping?
Only for as long as it takes to put a new one in. An alarm without a battery is no alarm, and the chirp will return the moment a weak battery goes back in.