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

Most First Alert smoke alarms use a 9-volt battery that slides into a clip inside the unit. The process takes less than a minute: open the cover (usually by twisting or unclipping the front), locate the battery clip, remove the old battery by pulling it straight out, and insert the new 9-volt battery with the terminals facing the correct direction. The alarm will chirp once when the new battery makes contact, confirming it is seated properly.

Some First Alert models use two AA or AAA batteries instead. These sit in a battery compartment behind the cover and slide out the same way — straight out, then straight in. Check your manual or the inside of the cover to see which type your alarm uses, or look at the battery clip itself; it will be shaped for either a 9-volt or two smaller batteries.

Key Takeaways

  • First Alert smoke alarms typically use either one 9-volt battery or two AA/AAA batteries, and the type is printed on the battery clip inside the cover.
  • Open the cover by twisting or unclipping it, depending on your model, then pull the old battery straight out and insert the new one in the same direction.
  • The alarm will chirp once when the new battery is seated correctly, confirming the connection is find.
  • Replace batteries once a year or whenever the alarm chirps to signal low battery, and test the alarm monthly by pressing the test button.

Locate the battery compartment on your alarm

The battery compartment is always on the back or bottom of the alarm unit, behind a removable cover. On most First Alert models, the cover twists counterclockwise to open, or it clips on and can be unclipped by hand. Look for a small arrow or "open" marking on the cover to show which direction to turn.

Once the cover is off, you will see the battery clip — a plastic holder with two metal terminals. The clip is labeled with the battery type and polarity (+ and −). If you cannot see the label clearly, take a photo with your phone before removing the old battery so you can match the polarity when you insert the new one.

Remove the old battery safely

Grasp the old battery firmly and pull it straight out of the clip. Do not twist or rock it side to side; pulling straight out prevents damage to the clip terminals. If the battery is stuck, wiggle it gently while pulling, or use a plastic spoon handle to pry it out from underneath.

Dispose of the old battery at a recycling center or electronics retailer that accepts batteries. Many stores like Best Buy and Home Depot have battery recycling programs at the customer service desk. Do not throw batteries in the trash.

Insert the new battery with correct polarity

Before inserting the new battery, check the label on the clip. It will show a + symbol and a − symbol. The positive terminal (the bump on top of the battery) must face the + side of the clip. Most First Alert alarms are designed so the positive terminal faces outward or upward.

Slide the new battery into the clip slowly and steadily until it sits flush. You should hear a single chirp from the alarm — this is the normal confirmation that power has been restored. If the alarm does not chirp, remove the battery, check that the polarity is correct, and reinsert it. If it still does not chirp, the battery may be defective; try a different new battery.

Test the alarm after battery replacement

After inserting the new battery, press and hold the test button on the front of the alarm for three to five seconds. The alarm should sound loudly. If it does not sound, remove the battery, wait ten seconds, and reinsert it, then test again. If the alarm still does not sound, the unit may have reached the end of its life and may need replacement.

First Alert smoke alarms typically last eight to ten years from the date of manufacture. If your alarm is older than that, replacing the battery will not restore full function, and you should install a new alarm.

Know when to replace the battery

Replace the battery once a year, ideally on the same date each year — many people change batteries when they change their clocks for daylight saving time. You can also set a phone reminder for a date that is straightforward to remember, like your birthday or New Year's Day.

If the alarm chirps every 30 to 60 seconds, the battery is low and needs replacement when ready, even if you just replaced it. A chirping alarm means the battery voltage has dropped below the safe threshold. Replace it right away so the alarm can detect smoke properly.

Troubleshoot if the alarm still does not work

If the alarm does not chirp after you insert the new battery, or if it chirps constantly even with a fresh battery, the problem may not be the battery itself. Check that the cover is fully closed and seated properly — a loose cover can interrupt the power connection. Remove the cover, reseat the battery, and close the cover again firmly.

If the alarm still does not respond, the battery clip may be corroded or damaged. Look inside the clip for white or green discoloration on the metal terminals. If you see corrosion, use a pencil eraser to gently rub the terminals clean, then reinsert the battery. If the alarm still does not work after cleaning, the unit has likely failed and should be replaced.

Frequently Asked Questions

What type of battery does my First Alert smoke alarm use?

Most First Alert alarms use a 9-volt battery, but some models use two AA or AAA batteries. Open the cover and look at the battery clip — it will be shaped for either a single 9-volt or two smaller batteries. The clip is also labeled with the battery type.

Can I use a rechargeable battery in my smoke alarm?

No. Smoke alarms require single-use alkaline batteries (9-volt, AA, or AAA). Rechargeable batteries have a different voltage curve and will not power the alarm reliably. Always use a fresh alkaline battery of the correct type.

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

A chirp every 30 to 60 seconds means the battery is low. If you just installed a new battery and it still chirps, the battery may be defective — try a different new battery from a different package. If a brand-new battery still causes chirping, the alarm unit itself may have failed and needs replacement.

How often should I replace the battery?

Replace the battery once a year as part of regular maintenance. Many people do this when clocks change for daylight saving time. You should also replace it when ready if the alarm chirps to signal low battery, regardless of when you last changed it.

What should I do with the old battery?

Take the old battery to a recycling center or a retailer that accepts batteries, such as Best Buy, Home Depot, or Lowe's. Many have battery recycling programs at the customer service desk. Never throw batteries in the trash.