Replace the battery in minutes with the right size and model number
Most First Alert smoke and carbon monoxide detectors use a 9-volt battery that slides or clicks into a compartment on the back or side of the unit. The exact steps depend on whether you have a hardwired detector with a battery backup or a battery-only model. The battery itself costs between $3 and $8, and the whole job takes less than five minutes once you have the replacement in hand.
First Alert detectors chirp or beep when the battery is low — usually once every 30 to 60 seconds — rather than failing silently. That warning gives you time to buy a replacement before the detector stops working. If your detector is chirping now, the battery is already weak and should be swapped out today.
Key Takeaways
- Most First Alert detectors use a standard 9-volt battery that you can buy at any drugstore, grocery store, or hardware retailer.
- The battery compartment is usually on the back or bottom of the unit and opens by sliding, twisting, or pressing a release tab.
- Write down your detector model number before you shop so you can confirm the battery type — a few older models use AA or 10-year sealed batteries instead.
- After you insert the new battery, press the test button to confirm the detector sounds; if it does not, the battery may not be seated correctly.
Locate your detector model number and battery type
The model number is printed on a label on the back or bottom of the detector. Write it down or take a photo. Common First Alert smoke detector models include the SA7010B, SC7010B, and 7010B; common carbon monoxide models include the CO400, CO605, and CO615. Each model uses a specific battery type, though most use a standard 9-volt.
Before you leave home to buy a battery, check the label on your detector or the original packaging if you still have it. The label usually says "9V" or lists the battery type directly. If you cannot find the label, you can search your model number on the First Alert website or call their customer service line to confirm what battery fits.
Buy the correct replacement battery
A standard 9-volt battery works in most First Alert detectors. Brands like Duracell, Energizer, and Amazon Basics all make 9-volt batteries that work equally well. Buy one battery at a time unless you have multiple detectors — there is no need to stock up, and batteries lose charge slowly even when not in use.
If your detector is older or uses a different battery type, the label will say so. Some First Alert models use AA batteries instead, and a few use sealed 10-year batteries that cannot be replaced. If you see "10-year" on the label, the entire detector needs to be replaced when the battery dies, not just the battery itself.
Open the battery compartment
Most First Alert detectors have a compartment on the back or bottom that opens one of three ways: by sliding a cover to the side, by twisting the cover counterclockwise, or by pressing a release tab or button. Look for arrows or text on the compartment that shows which direction to move it. Do not force it — if it does not slide or twist easily, you may be pushing in the wrong direction.
If the compartment is stuck, try gently prying the edge with a plastic spoon or old credit card rather than a metal tool, which can scratch the detector. Once the compartment opens, you will see the battery holder — usually a plastic clip or slot that holds the 9-volt upright.
Remove the old battery and insert the new one
Grip the old battery by its sides and pull it straight out of the holder. Do not touch the metal terminals on the top and bottom of the battery. Slide or press the new battery into the holder with the positive terminal (marked with a plus sign) facing up. You should hear or feel a click when the battery seats fully.
If the battery does not click or sit flush, remove it and try again. A battery that is not seated correctly will not power the detector. Once the battery is in place, close the compartment by sliding, twisting, or pressing it back into position until it clicks or locks.
Test the detector to confirm it works
Press and hold the test button on the front of the detector for three to five seconds. The alarm should sound loudly — a loud beep for smoke detectors or a pattern of beeps for carbon monoxide detectors. If the alarm sounds, the battery is installed correctly and the detector is working.
If the alarm does not sound, open the compartment again and check that the battery is seated all the way in the holder. Remove it, wait a few seconds, and reinsert it. Then test again. If the detector still does not sound after a second attempt, the battery may be defective or the detector itself may need to be replaced.
When to replace the entire detector instead of just the battery
First Alert smoke detectors typically last 8 to 10 years, and carbon monoxide detectors last 5 to 7 years. If your detector is older than that and the battery is low, replacing the battery alone may not be worth it — the detector itself is nearing the end of its useful life. Check the manufacture date on the back of the unit; if it is more than a decade old, buy a new detector.
If the detector is newer but does not sound when you press the test button even after replacing the battery, the internal sensors may have failed. In that case, the detector should be replaced rather than repaired. First Alert detectors are inexpensive — usually $15 to $40 — and replacement is safer than keeping a faulty unit in place.
Frequently Asked Questions
Can I use a rechargeable 9-volt battery in my First Alert detector?
Rechargeable 9-volt batteries work in most First Alert detectors, but they lose charge faster than alkaline batteries and may not power the detector for as long. Alkaline batteries are cheaper and more reliable for this use. If you do use a rechargeable battery, test the detector monthly to make sure it still sounds.
What should I do with the old battery?
Take used 9-volt batteries to a battery recycling program or a retailer that accepts them — most electronics stores, office supply stores, and some grocery stores have drop-off bins. Do not throw batteries in the trash. Your local waste management website can tell you where the nearest recycling location is.
Why is my detector still chirping after I put in a new battery?
The battery may not be seated all the way in the holder. Open the compartment, remove the battery, and reinsert it firmly until you hear a click. If it still chirps after that, try a different new battery — the first one may be defective. If a brand-new battery does not stop the chirping, the detector itself may need to be replaced.
How often should I replace the battery in my First Alert detector?
Most 9-volt batteries last 6 to 12 months in a detector, depending on the model and how often the detector tests itself. You do not need to replace it on a schedule — just replace it when the detector chirps. Some people change batteries twice a year as a precaution, usually when they change their clocks for daylight saving time.