Replace the battery in under two minutes

Most First Alert smoke and carbon monoxide detectors use a 9-volt battery that slides or clicks into place on the back or side of the unit. To change it, press the release tab or button (usually marked with an arrow), pull the old battery straight out, and slide a fresh 9-volt battery in until you hear a click. The detector will chirp once to confirm the new battery is seated correctly. The whole job takes about 30 seconds of actual work.

The tricky part is not the battery swap itself—it is knowing when to do it. First Alert detectors chirp every 30 to 60 seconds when the battery is low, and that chirp will not stop until you replace it. Some models also have a low-battery light that blinks red. Do not ignore these signals. A detector with a dead battery cannot alert you to smoke or carbon monoxide, which defeats the entire purpose of having one.

Key Takeaways

  • First Alert detectors use standard 9-volt batteries that cost $5 to $10 and are sold at any drugstore or hardware store.
  • A chirping detector every 30 to 60 seconds means the battery is low and needs replacement within a day or two.
  • The battery slides or clicks into a slot on the back or side of the unit—check your model's label if you cannot find it.
  • After you insert the new battery, the detector should chirp once to confirm it is working; if it does not chirp at all, the battery may not be seated correctly.
  • Replace batteries once a year even if they have not started chirping, ideally when you change your clocks for daylight saving time.

Locate the battery compartment on your detector

The battery slot is almost always on the back or bottom of the unit. Look for a small rectangular opening or a tab labeled "Battery" with an arrow pointing in the direction you should pull. On some older First Alert models, the compartment is on the side. If you cannot find it by looking, check the label on the back of the detector or the original packaging—it will show you exactly where the slot is.

Do not pry or force anything. If the compartment does not open easily, you may be looking at the wrong spot. Take the detector down from the wall or ceiling if you need to see it better. Most detectors are held by a single screw or a clip, and removing it for 30 seconds is worth the certainty that you are working on the right part.

Remove the old battery and insert the new one

Press or slide the release tab in the direction the arrow points. The old battery should come free in your hand. If it is stuck, do not yank it—wiggle it gently side to side while pulling. Once it is out, note which way the terminals face (the flat metal end should face outward on most models, but check the slot itself for a diagram).

Slide the new 9-volt battery into the slot with the terminals facing the same direction the old one faced. Push it in until you feel a click or hear a snap. The battery should sit flush with the detector body, not sticking out. If it does not click, pull it out and flip it around—you may have inserted it backwards. Once it is seated, the detector will usually chirp once or twice to confirm the battery is working.

Confirm the battery is working correctly

Listen for a single chirp within a few seconds of inserting the battery. That chirp means the detector recognizes the new battery and is powered on. If you hear nothing, remove the battery, check that the terminals are clean (wipe them with a dry cloth if they look corroded), and reinsert it. If the detector still does not chirp, try a different 9-volt battery—the first one may be defective.

Do not test the detector by holding down the test button right after changing the battery. Wait at least 30 seconds. The test button triggers the alarm to confirm the speaker works, and doing it when ready after a battery change can confuse the detector's electronics. After 30 seconds, press and hold the test button for three to five seconds. The alarm should sound loudly. If it does not, the detector itself may need replacement.

Know when to replace batteries on schedule

Even if your detector is not chirping, replace the battery once a year. A good time to do this is when you change your clocks for daylight saving time in spring and fall—pick one of those dates and stick to it. Batteries lose power gradually, and waiting for the chirp means you are running on a weakening battery for weeks before you notice.

Buy 9-volt batteries in bulk if you have more than one detector. A pack of four costs less than $15 and means you will always have a fresh battery on hand. Store them in a cool, dry place—not in a damp bathroom or near a heat source. Batteries stored in extreme temperatures lose power faster.

Troubleshoot a detector that keeps chirping

If the detector chirps even after you have installed a new battery, the battery may not be fully seated. Remove it, look at the slot to make sure nothing is blocking it, and reinsert the battery with firm, steady pressure until you hear the click. If it still chirps, try a different brand of 9-volt battery—some detectors are picky about which brands they accept, though any standard 9-volt should work.

If a new battery stops the chirping for a few days and then it starts again, the detector's internal circuitry may be failing. First Alert detectors typically last 5 to 10 years. If yours is older than that and the battery is fresh, replacement is the safest option. A detector that cannot hold a charge or that chirps unpredictably is not reliable.

Frequently Asked Questions

What type of battery does a First Alert detector use?

Most First Alert smoke and carbon monoxide detectors use a standard 9-volt battery. Check the label on the back of your unit to confirm, as a small number of older models use AA or AAA batteries instead. The label will also tell you the exact model number if you need to look up the battery type online.

Why does my detector keep chirping even with a new battery?

The battery may not be clicked all the way in. Remove it, inspect the slot for debris, and reinsert it with firm pressure until you hear a definite click. If it still chirps, the detector's internal sensor may be failing, especially if the unit is more than five years old. A failing detector should be replaced.

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 reliably during a power outage. Stick with standard alkaline 9-volt batteries for consistent performance. Rechargeable batteries are better suited to devices you use frequently and can recharge regularly.

How long does a 9-volt battery last in a smoke detector?

A fresh alkaline 9-volt battery typically lasts 6 to 12 months in a smoke or carbon monoxide detector, depending on how often the detector runs its self-test and how much the alarm has sounded. This is why replacing the battery once a year on a set schedule is safer than waiting for the chirp.

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 center, an electronics store like Best Buy, or a hazardous waste collection event in your area. Many hardware stores and drugstores also accept used batteries for free recycling. Check Earth911.com or your city's waste management website to find a drop-off location near you.