The basic steps to replace a First Alert smoke detector battery

Most First Alert smoke detectors use a 9-volt battery that slides or clicks into a compartment on the back or bottom of the unit. To change it, press the test button on the front of the detector while holding it steady, then twist the detector counterclockwise (or pull it straight down, depending on your model) to remove it from the ceiling or wall mount. Once the detector is in your hand, locate the battery compartment — usually marked with a battery symbol — and slide or pop out the old battery. Insert the new 9-volt battery with the terminals facing the correct direction (the label on the compartment shows which way), then reinstall the detector by twisting it clockwise or pushing it back onto the mount until it clicks.

After you install the new battery, press and hold the test button for three to five seconds. You should hear a loud alarm sound — this confirms the battery is working and the detector is functioning. If you hear nothing, the battery may be installed backwards or the detector itself may need replacement.

Key Takeaways

  • First Alert smoke detectors typically use a single 9-volt battery located in a compartment on the back or bottom of the unit.
  • Remove the detector from its mount by twisting counterclockwise or pulling straight down, depending on whether it screws or clips into place.
  • Slide or pop out the old battery and insert the new one with the terminals facing the direction shown on the compartment label.
  • Test the detector when ready after installation by pressing the test button for three to five seconds and listening for the alarm sound.

Where the battery compartment is located on different First Alert models

The battery compartment location varies slightly between First Alert models. On many hardwired models with battery backup, the compartment is on the back of the unit and opens with a small latch or slide. On battery-only models, the compartment is often on the bottom. Check your specific model number — usually printed on the back or bottom of the detector — against the First Alert website or your manual to confirm the exact location before you start.

If you cannot find the compartment, look for a small rectangular outline or a battery symbol printed on the detector's casing. Some models require you to remove a cover plate first, which may be held by a single screw or straightforward snapped in place.

Choosing the right replacement battery

First Alert smoke detectors almost always use a standard 9-volt battery. You can buy these at any grocery store, pharmacy, hardware store, or online retailer for between $3 and $8 per battery. Alkaline 9-volt batteries are the most common and work in all First Alert models. Lithium 9-volt batteries last longer (up to 10 years versus 5 years for alkaline) but cost more — typically $8 to $15 per battery.

Check the label on your detector or in your manual to confirm the voltage before you buy. A few older First Alert models use AA or AAA batteries instead, though this is less common. If you are unsure, remove the old battery and bring it to the store to match it exactly.

How often to replace the battery

Most First Alert detectors will chirp or beep once every 30 to 60 seconds when the battery is running low. This sound usually starts when the battery has about 30 days of charge left. When you hear this chirp, replace the battery within the next week. Do not ignore the chirp — a detector with a dead battery cannot alert you to smoke or fire.

If your detector does not chirp but straightforward stops working, the battery may have died suddenly. This is rare with alkaline batteries but can happen. If you have not changed the battery in more than five years, replace it now even if the detector seems to be working.

Hardwired detectors with battery backup

If your First Alert detector is hardwired into your home's electrical system, it may have a battery backup compartment. These detectors run on household power but keep a 9-volt battery on hand in case of a power outage. The battery compartment is usually on the back of the unit and opens the same way as a battery-only model. You still need to replace this backup battery every five years or when the detector chirps.

To change the battery in a hardwired detector, you do not need to turn off the power to your home. straightforward remove the detector from its mount, open the battery compartment, and swap out the old battery for a new one. The detector will continue to run on household power during the swap.

Troubleshooting when the detector still does not work after battery replacement

If you installed a new battery and the detector still does not beep when you press the test button, first check that the battery is installed correctly. Remove it and look at the compartment label — the positive and negative terminals must match the battery's terminals. Reinstall it and test again.

If the detector still does not work, try a different new battery to rule out a defective one. If a second battery also fails to trigger the alarm, the detector itself may be faulty and need replacement. First Alert detectors typically last 8 to 10 years; if yours is older than that, replacement is usually the best option. If your detector is newer and still under warranty, contact First Alert customer service with your model number and purchase date.

Frequently Asked Questions

Can I use a different type of battery in my First Alert detector?

No. First Alert detectors are designed for a specific battery type — almost always a 9-volt alkaline or lithium battery. Using the wrong type can damage the detector or cause it to malfunction. Always check your manual or the compartment label to confirm the correct battery before you buy.

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

Take the old battery to a battery recycling program or a store that accepts batteries for recycling. Many retailers that sell batteries — including Best Buy, Home Depot, and Lowe's — accept used batteries for free. Do not throw it in the trash, as batteries contain materials that can harm the environment.

Why does my detector keep chirping even after I put in a new battery?

The chirp may continue for a few minutes after you install a new battery while the detector resets. If it chirps for more than 10 minutes, remove the battery, wait 30 seconds, and reinstall it. If the chirping continues after that, the detector may be faulty and need replacement.

Do I need to turn off power to my home to change the battery in a hardwired detector?

No. Hardwired detectors run on household power, so the battery change does not affect the main electrical system. You can safely remove and replace the battery backup without turning off any breakers.

How do I know if my detector is battery-only or hardwired?

Look at the back of the detector. If you see wires connected to it, it is hardwired. If there are no wires and only a battery compartment, it is battery-only. Hardwired detectors are usually mounted in the center of a ceiling or hallway, while battery-only models can be mounted anywhere.