Replace the battery by opening the alarm cover, removing the old battery, and inserting a new one of the same type

Most First Alert smoke alarms use a 9-volt battery as a backup power source. To replace it, you open the alarm cover (usually by twisting or unclipping it), slide out the old battery, and insert a new 9-volt battery with the terminals facing the correct direction. The whole job takes less than a minute. Your alarm will beep once when you close the cover if the battery is installed correctly.

Some First Alert models are hardwired to your home's electrical system but still have a battery backup. Others run on battery alone. Either way, the replacement process is the same. The alarm will chirp every 30 to 60 seconds when the battery is low — that's your signal to replace it.

Key Takeaways

  • First Alert smoke alarms typically use a standard 9-volt battery that you can buy at any drugstore or hardware store for a few dollars.
  • Open the alarm cover by twisting it counterclockwise or pressing the release tabs on the sides, depending on your model.
  • Insert the new battery with the positive terminal (marked with a +) facing up into the connector, then close the cover until you hear a click or beep.
  • If the alarm continues to chirp after you install a new battery, the battery may not be seated properly or the alarm itself may need replacement.
  • Replace batteries in all your smoke alarms at the same time so you don't have to climb back up in a few weeks.

What type of battery your First Alert alarm uses

The vast majority of First Alert smoke alarms use a single 9-volt battery. You can identify it by its rectangular shape and two metal terminals on top. A 9-volt battery costs between $3 and $8 depending on the brand and where you buy it. Duracell and Energizer are the most common brands, but any 9-volt battery will work in your alarm.

A few older First Alert models or specialty alarms may use AA or AAA batteries instead. Check the label on the back of your alarm or open the cover to see what's inside. The battery compartment will be clearly marked with the size you need.

How to open the alarm cover safely

First Alert alarms have two common cover designs. The most frequent type twists off: grip the outer ring of the alarm and turn it counterclockwise until the cover separates from the base. The second type has a release button or tab on the side — press it and the cover will pop off or slide down.

If you're not sure which type you have, look for a seam around the middle of the alarm. If the seam runs horizontally all the way around, it twists. If you see a small button or slot on the side, press or slide it. Never pry the cover with a screwdriver, as you can crack the plastic.

Once the cover is off, you'll see the battery connector — a small plastic clip with two metal contacts inside. The old battery will be sitting in or near this connector.

Removing the old battery and inserting the new one

Gently pull the old battery straight out of the connector. If it's stuck, wiggle it slightly side to side as you pull. Don't force it, as the connector can break if you yank too hard.

Before you insert the new battery, check the polarity markings inside the alarm cover or on the connector itself. The positive terminal (marked +) should face up or toward the top of the alarm. The negative terminal (marked −) faces down. Slide the new battery into the connector until it clicks or sits snugly. The battery should not be loose or fall out when you tilt the alarm.

Close the cover by twisting it clockwise (if it twists) or pressing it back into place (if it clips). You should hear a single beep or chirp when the cover closes completely. That beep confirms the battery is installed correctly and the alarm is working.

What to do if the alarm keeps chirping after you replace the battery

A continuous chirp every 30 to 60 seconds after battery replacement usually means the battery is not making good contact with the connector. Open the cover again, remove the battery, and check both the battery terminals and the metal contacts inside the connector for dirt, corrosion, or damage. Wipe them gently with a dry cloth and reinsert the battery.

If the alarm still chirps, try a different new battery — the one you installed may be defective. If a second battery also produces the same chirping, the connector itself may be damaged and the alarm may need to be replaced. First Alert alarms typically last 8 to 10 years, so if your alarm is older than that, replacement is often cheaper than troubleshooting.

When to replace the entire alarm instead of just the battery

If your First Alert alarm is more than 10 years old, the sensor inside may no longer detect smoke reliably, even if the battery works fine. Check the date printed on the back of the alarm. If it's older than a decade, buy a new alarm rather than continuing to replace batteries in a device that may not protect you.

You should also replace the alarm if it chirps constantly even after you've tried two new batteries and cleaned the connector, or if it goes off randomly without smoke present. A faulty alarm is worse than no alarm because it trains you to ignore the sound.

Frequently Asked Questions

Can I use a rechargeable 9-volt battery in my First Alert smoke alarm?

Rechargeable 9-volt batteries work in First Alert alarms but are not recommended. They hold less charge than alkaline batteries and may not provide enough power during a fire. Stick with standard alkaline 9-volt batteries from Duracell, Energizer, or a store brand.

Why does my alarm chirp even though I just put in a new battery?

The battery may not be seated properly in the connector. Open the cover, remove the battery, and reinsert it firmly until you hear a click. If it still chirps, the connector may be dirty — wipe the metal contacts with a dry cloth. If a second new battery also chirps, the alarm likely needs replacement.

How often should I replace the battery in my smoke alarm?

Most 9-volt batteries last 6 to 12 months in a smoke alarm, depending on the brand and whether the alarm is hardwired or battery-powered. Replace the battery as soon as you hear the low-battery chirp. Many people replace all their smoke alarm batteries twice a year on a set schedule, like when they change their clocks for daylight saving time.

What should I do with the old battery after I remove it?

Do not throw a used 9-volt battery in the trash. Take it to a battery recycling program at your local hardware store, electronics retailer, or municipal hazardous waste facility. Many stores like Best Buy and Home Depot accept old batteries for free.

Is it normal for the alarm to beep once when I close the cover?

Yes. A single beep when you close the cover means the battery is installed correctly and the alarm is powered. If you hear no beep or a series of chirps, the battery may not be seated properly — open the cover and try again.