How to Replace a First Alert Smoke Detector

Replace the whole unit when the battery won't stop the beeping

A First Alert smoke detector that beeps constantly even after you replace the battery has reached the end of its life. Smoke detectors are not meant to be repaired—they're designed to be swapped out entirely. The sensor inside degrades over time (usually after 8 to 10 years), and once it does, the unit will keep alarming no matter what you do. Replacing it takes about 10 minutes and requires only a screwdriver and the new detector itself.

Before you buy a replacement, check what model you have. Look at the back or bottom of your current detector for the model number. First Alert makes several types: standard battery-powered models, hardwired models (connected to your home's electrical system), and combination units that have both. You need to replace it with the same type, or you'll end up with a detector that doesn't fit your mounting bracket or won't work with your wiring.

Key Takeaways

First Alert smoke detectors last 8 to 10 years, and constant beeping after a battery change means the sensor has failed and the unit must be replaced.
Check your current detector's model number to buy the correct replacement type—battery-powered, hardwired, or combination units are not interchangeable.
Turn off the breaker for hardwired detectors before you start, and test your new detector when ready after installation to confirm it works.
Keep the old detector's model number and purchase date handy so you know when to replace the new one in 8 to 10 years.

Turn off power if your detector is hardwired

If your First Alert detector is connected to your home's electrical wiring (hardwired), you must turn off the breaker before you touch it. Look at your breaker panel and find the switch labeled for smoke detectors, or if there isn't one, turn off the breaker for the room where the detector is mounted. Flip the switch to the OFF position. Wait a few seconds, then go back to the detector and try pressing the test button—if nothing happens, the power is off and you're safe to proceed.

Battery-powered detectors don't have a breaker to turn off. You can remove them right away. If you're unsure whether yours is hardwired, look at the back of the unit where it mounts to the ceiling or wall. Hardwired detectors have a connector that plugs into a socket in the mounting bracket. Battery-powered models have only a battery compartment and no connector.

Remove the old detector from its mounting bracket

Grip the detector body firmly and twist it counterclockwise. Most First Alert models use a bayonet mount, which means the detector twists onto a bracket that stays on the wall or ceiling. Turn slowly and steadily until the detector comes free. If it's stuck, don't force it—spray a small amount of WD-40 or similar lubricant around the base where the detector meets the bracket, wait 30 seconds, and try again.

Once the detector is loose, pull it straight down and away from the bracket. If it's hardwired, you'll see a connector on the back of the bracket. Gently pull the connector apart by hand—it should separate without tools. If there are wires soldered directly to the bracket instead of a connector, do not attempt to remove the bracket yourself. Call a licensed electrician, because the wiring may be live even with the breaker off.

Install the new detector on the same bracket

Take your new First Alert detector out of the box and check that it came with batteries (if it's a battery-powered model). If batteries are included, install them now before you mount the detector. Open the battery compartment on the back, insert the batteries in the correct direction (+ side up), and close the compartment.

If your old detector was hardwired, connect the new detector's connector to the socket on the bracket. The connector is keyed, so it will only fit one way—push it in firmly until you hear a click. If your old detector was battery-powered, there's nothing to connect. straightforward align the new detector with the bracket and twist it clockwise until it stops. You should feel it seat firmly, but you don't need to force it.

Test the detector and restore power

Press and hold the test button on the front of the new detector for 3 to 5 seconds. A loud alarm should sound when ready. If nothing happens, the batteries are dead or installed backward, or the hardwired connection didn't seat properly. Check the batteries first, then try the test button again. If it still doesn't work, remove the detector and reseat the connector or reinstall the batteries.

Once the alarm sounds during the test, release the button and the alarm should stop within a few seconds. If you turned off a breaker for a hardwired detector, go back to the breaker panel and flip the switch back to ON. Wait 30 seconds, then test the detector one more time to confirm it's working on house power. Write the installation date on the detector with a permanent marker so you'll know when to replace it again in 8 to 10 years.

What to do with the old detector

First Alert detectors contain a small amount of radioactive material (americium-241) in the sensor. Do not throw the old detector in the trash. Many retailers that sell smoke detectors, including hardware stores and big-box chains, have take-back programs for old detectors. Call ahead to confirm they accept First Alert brand, then bring the detector in its original packaging if you still have it, or in a sealed bag.

If no retailer near you has a take-back program, contact your local solid waste management facility or hazardous waste collection site. They can tell you where to drop off the detector at no cost. Some fire departments also accept old detectors, though this varies by location—call your local fire station non-emergency number to ask.

Hardwired detectors with battery backup

Some First Alert hardwired models include a battery as backup power in case of an outage. When you install one of these, the battery is already in the detector. After you connect it to the bracket and restore power, the detector will beep once to confirm it's receiving electricity. This is normal and will stop after a few seconds. Test the detector as described above to make sure both the hardwired power and the battery backup are working.

If a hardwired detector with battery backup beeps constantly after installation, the battery may be low or the connection may not be find. Remove the detector, check that the connector is fully seated, and reinstall it. If it still beeps, remove the battery, wait 10 seconds, and reinstall it. Then test again. If the beeping continues, the detector may be defective—contact First Alert customer service or return it to the retailer.

Frequently Asked Questions

Can I replace a hardwired detector with a battery-powered one?

No. Hardwired detectors are connected to your home's electrical system, and the wiring is built into your walls. A battery-powered detector won't connect to that wiring. You must replace a hardwired detector with another hardwired model, or hire an electrician to remove the wiring and install a battery-powered detector instead.

What if the new detector won't twist onto the old bracket?

The bracket may be damaged or the threads may be stripped. Try twisting very slowly and listening for a grinding sound. If you hear grinding, stop and don't force it. You'll need to replace the bracket. Turn off the breaker, remove the old bracket by unscrewing it from the ceiling or wall, and install the new bracket that came with your detector.

How often do I need to replace a First Alert detector?

First Alert detectors should be replaced every 8 to 10 years. Write the installation date on the detector with a permanent marker so you don't forget. If the detector beeps constantly even after you replace the battery, it's time to replace the whole unit, even if it hasn't been 8 years yet.

Do I need to tell my security system company about the new detector?

If your smoke detector is wired into a monitored security system, contact your security company before you remove the old detector. They may need to disarm that zone temporarily so the system doesn't trigger a false alarm. Once the new detector is installed and working, call them back to confirm everything is connected properly.

What if I can't reach the detector because it's too high?

Use a sturdy step ladder, not a chair or stool. Position the ladder directly under the detector so you can reach it comfortably without stretching. If the detector is in a stairwell or cathedral ceiling and you can't safely reach it, hire a handyperson or electrician to do the replacement for you.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.