Alarm adapter (depending on your original and new alarm model)
Wire stripper (optional)
Wire nuts (optional)
Electrical tape (optional)
Batteries
It’s easy to get complacent about fire hazards hiding in your home and forget about replacing smoke alarms—unless you’re constantly setting them off when you burn your morning toast. However, according to the National Fire Protection Association, from 2014 to 2018, 41% of fire fatalities were in homes with no smoke alarms and 16% in properties with smoke alarms that failed to operate.
To provide peace of mind, regularly test your detectors and swap them out before they’re likely to go on the fritz. Thankfully, learning how to replace a smoke detector is something even the least handy homeowners can usually tackle.
Prepping to Replace a Smoke Detector
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Most modern smoke detectors are hardwired to your home’s electrical system with a backup battery. Less commonly, alarms are powered only by battery. This step-by-step guide focuses on how to replace a hardwired smoke detector.
Before you buy replacement hardwired smoke detectors, there are a few things to do:
Establish smoke detector locations: Make sure you know the placement of smoke alarms in your home so you don’t forget about any.
Confirm replacement dates: Most smoke alarms last ten years. Reputable hardwired models have the date of manufacture on them so you know when they need replacing.
Test existing devices: Even if your alarm isn’t due for immediate replacement, test detectors regularly. And if the alarm is making a warning chirp, this is another indicator it needs replacing—or at least the backup batteries do.
Know how many alarms you need to replace: Some smoke detector systems are interconnected, and you might need to change all the devices at once or have one compatible replacement to keep all the other devices working correctly.
Pick an appropriate new model: To avoid having to replace the mount or doing complicated rewiring, purchase a new smoke detector compatible with the old version. Alternatively, buy a wire adapter to apply while fitting.
Check manufacturer’s instructions: Read the instructions that come with the model you have to ensure there isn't any bespoke installation guidance.
Turn Off the Power
Always turn off the power on the linked circuit breaker before replacing a smoke detector. It might be marked “fire alarm” or could be on the same circuit as the room lighting.
Remove the Old Smoke Detector From the Mounting Bracket
Most of the time, you can simply twist the old alarm out of the mounting bracket. It’s ready to pull free when you hear a click. If the old mounting bracket isn’t compatible with the new detector, you might need to loosen the screws with your screwdriver and remove the bracket to replace it with a new one.
Disconnect the Wiring (If You Don’t Have an Adapter)
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If you don’t have a compatible wiring harness or adapter, disconnect the old detector wiring first. There will be two or three wires. A 120-volt black wire, a neutral white wire, and there might be a red or yellow wire that is used if you have a multi-alarm system that is interconnected.
To release the wires, squeeze the side of the harness plug. You may need to remove electrical tape or wire caps before untwisting and removing the harness to expose the metal ends of the wires.
Connect and Secure the New Smoke Detector
You won’t need to strip the wiring if you have a compatible detector. You’ll simply need to remove the old alarm from the mounting bracket and disconnect it from the wiring harness box. You can then connect the new alarm to the wiring harness. Don’t forget to add or activate the backup battery if the detector has this feature.
If the wiring harness isn’t a match, you might be able to plug it into an adapter to connect to your new smoke detector and save you from fiddling around with the wiring.
If you have some experience with electrical work, you can carefully match up and twist the wires of the new alarm together with the exposed ones of the same color before replacing the wiring harness and adding new electrical tape or putting the wire caps back on.
Pair the black-to-black wire, white-to-white, and red-to-red or yellow-to-yellow. If you have a yellow wire on the new alarm, but the old wiring is red, twist these two together. You might need to use a wire stripper and wire nuts to expose enough wire and secure the connection. Note: Do not play with the wires if you’re not confident in what you’re doing. Electrical work can be dangerous, so call in a local electrician to help you if you need it.
Reinstall the Mounting Bracket
You can now click the smoke detector back into the mounting bracket. Alternatively, if the bracket isn’t compatible with the new alarm, you might need to screw in the new one.
Turn the Power Back On and Test
Once the wiring is securely connected, turn the power back on at the circuit breaker. Your new alarm might beep, and an LED light could indicate everything is good to go. Warn everyone at home before pressing the test button on the new smoke detector to check it's functioning properly.
If the alarm doesn’t work, check if you flipped the right breaker switch. If it still doesn’t work, you can turn the power off again and check all the wire connections. Still not working? It might be worth asking for a replacement from the retailer before calling the pros.
DIY vs. Hiring a Pro
Replacing a smoke detector is an easier DIY job than learning how to install a smoke alarm system from scratch, especially if you have a compatible wire harness or adapter because the wiring is already in place. However, if you aren’t confident working with electrical (or can’t reach the smoke detector), you have a few different pros that can help.
You can call an alarm company near you or a local electrician to assist. The cost to install a smoke detector professionally ranges from $70 to $150 for a hardwired device. Or, a local handyman can help to replace your hardwired smoke detector at a price that might be lower than that of an electrician. It’s important to note that firefighters in most areas can install battery-operated smoke alarms in your home at no cost, but when it comes to hardwired units, calling in a pro is your best bet if you’re not taking the DIY route.
Frequently Asked Questions
Your smoke detector might be too high in some homes or circumstances to reach yourself. If you feel unsafe getting on a ladder to replace your hardwired smoke detector, call a licensed electrician or local handyman to knock this project off your to-do list. If you have a battery-operated smoke detector, your local fire department can change the batteries or help you replace the detector—just make sure you call the non-emergency number.
In any case, do not let this project go unresolved, as it could turn into a huge safety issue.
If your hardwired smoke alarm keeps going off, it could be because the backup battery needs replacing. When replacing the battery doesn’t stop your smoke alarm from beeping, try holding the reset button for 15 to 30 seconds or removing dust from the openings in the alarm. If it continues to chirp, it could be faulty and require replacement.
You can temporarily unplug a wired fire alarm (don’t forget to take out the backup battery as well), but this is generally only recommended when it’s faulty and won’t stop chirping. It’s safer to turn off the circuit breaker first and remember all alarms might stop working for interconnected systems. Don’t leave a fire alarm unplugged for extended periods. Troubleshoot, replace the alarm, or call the professionals ASAP.
It’s critical to your safety to replace your hardwired smoke detector every 10 years from the date of installation. It’s just as important to test your smoke detectors at least once per month to make sure they are functioning correctly. If they don’t respond properly when tested, it’s best to replace it, even if it is before the 10-year mark.
If you have a battery-operated smoke alarm, how often you need to pop it open and change the batteries depends on the model and type of batteries. Those with nine-volt or AA batteries might need changing once or twice a year, and lithium batteries can last up to a decade.
Gemma has been a freelance writer and editor in the home and lifestyle space for the past five years and has a bachelor's degree in communication studies.
Gemma has been a freelance writer and editor in the home and lifestyle space for the past five years and has a bachelor's degree in communication studies.
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