Replace the battery in under two minutes

Most First Alert smoke 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 test button on the front — if the alarm sounds weak or doesn't sound at all, the battery is dead. Remove the old battery, insert a new 9-volt battery with the terminals facing the correct direction, and test again. The whole job takes less than two minutes.

First Alert makes several detector models, and the battery location varies slightly between them. Hardwired models with battery backup have the battery compartment on the back. Wireless models and battery-only detectors have it on the side or bottom. The process is the same for all: locate the compartment, remove the old battery, and install the new one.

Key Takeaways

  • Most First Alert detectors use a standard 9-volt battery that you can buy at any drugstore or hardware store for $5 to $10.
  • Press the test button before you change the battery to confirm it is actually dead and not just low.
  • The battery compartment is usually on the back or side of the unit and opens by sliding or unclipping a small cover.
  • After you insert the new battery, press the test button again to make sure the alarm sounds loud and clear.
  • Replace the battery once a year, or whenever the detector chirps every 30 to 60 seconds — that chirp is the low-battery warning.

Locate the battery compartment on your model

The battery compartment location depends on which First Alert detector you own. On hardwired models with battery backup — the kind wired into your home's electrical system — the battery compartment is on the back of the unit. On battery-only detectors and wireless models, it is usually on the side or bottom. Look for a small rectangular cover or a slot where the battery slides in.

If you cannot find the compartment, check the model number on the front or back of the detector and search for the manual online. First Alert publishes PDFs for most models on their website, and the manual will show you exactly where the battery goes. The model number is usually printed in small text near the test button or on the back.

Remove the old battery and insert the new one

Open the battery compartment by sliding the cover to the side or unclipping it — most First Alert detectors use a straightforward plastic clip that requires only a gentle pull. The old 9-volt battery will be sitting in a plastic holder or slot. Grasp the battery by the sides (not the terminals) and pull it straight out.

Take your new 9-volt battery and look at the terminals on top — one is marked with a plus sign and one with a minus sign. Insert the battery into the holder with the plus terminal facing up and the minus terminal facing down. You will hear or feel a small click when it seats correctly. Do not force it; if it does not slide in smoothly, flip the battery around and try again.

Test the detector after you install the battery

Once the new battery is in place, press and hold the test button on the front of the detector for three to five seconds. The alarm should sound loud and clear — a steady beeping or chirping noise. If it sounds weak or does not sound at all, remove the battery and check that the terminals are facing the right direction. Reinsert it and test again.

If the alarm still does not sound after you have tried twice, the detector itself may be faulty. First Alert detectors typically last 10 years from the manufacture date, which is printed on the back. If your detector is older than that, replace the entire unit rather than troubleshooting the battery further.

When to change the battery and what the warning sounds like

Change the battery once a year, ideally on the same day each year — many people do it when they change their clocks for daylight saving time. However, your detector will tell you when the battery is actually running low. A low battery produces a single chirp or beep every 30 to 60 seconds, separate from the full alarm sound you hear when you press the test button.

That chirp is annoying on purpose — it is designed to get your attention so you replace the battery before it dies completely. Do not ignore it or remove the battery to stop the noise. A detector without a working battery cannot protect you in a fire. Buy a 9-volt battery and change it as soon as you hear the chirp.

Buy the right battery type and keep spares on hand

First Alert detectors use a standard 9-volt battery, the same size you can find at any drugstore, supermarket, or hardware store. Brands like Duracell, Energizer, and Amazon Basics all work fine. A single battery costs between $5 and $10, depending on the brand and where you buy it. Buying a multi-pack is cheaper per battery if you have several detectors in your home.

Keep at least one spare 9-volt battery in a drawer or cabinet near your detectors so you do not have to run out when you hear the low-battery chirp. If you have detectors in multiple rooms, keep a spare near each one. Batteries last for years in storage, so buying extras now means you will always have one ready.

Frequently Asked Questions

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

Rechargeable 9-volt batteries work in First Alert detectors, but they hold less charge than alkaline batteries and may not last as long between changes. Stick with standard alkaline 9-volt batteries for the most reliable performance. If you do use a rechargeable battery, test the detector more often to make sure it is still working.

What if my detector chirps even after I put in a new battery?

A new battery should stop the chirping when ready. If it does not, remove the battery and reinsert it to make sure it is seated correctly. If the chirping continues, the detector itself may be faulty or at the end of its life. First Alert detectors last about 10 years; if yours is older, replace the entire unit.

Do I need to turn off power before changing the battery in a hardwired detector?

No. Hardwired detectors stay connected to your home's electrical system, and changing the battery does not interrupt that connection. You can safely remove and replace the battery without turning off any breakers. The battery is only a backup in case of a power outage.

How do I know which way the battery terminals should face?

The 9-volt battery has a plus sign and a minus sign on the terminals at the top. The plus terminal should face up into the detector, and the minus terminal should face down. Most First Alert detectors have a diagram inside the battery compartment showing the correct direction. If you do not see one, check the manual online using your model number.

What should I do with the old battery?

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 recycling. Call ahead to confirm they take 9-volt batteries.