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Smoke detectors are one of those products most people ignore until one starts chirping in the middle of the night. Then you discover that the alarm on your ceiling may be ten years old, the battery may not be replaceable, and the replacement choices are much more complicated than they look.

I recently went through exactly that problem when one of my hardwired alarms reached the end of its life. That sent me back into the current smoke-alarm market, which has changed considerably.

You can now choose between hardwired alarms with 10-year backup batteries, battery-only combination units, voice alerts, wired interconnection, phone notifications, Ring integration and smart alarms designed to replace Google Nest Protect.

Quick answer: If I needed a conventional hardwired smoke and carbon monoxide alarm today, I would start with the Kidde 30CUA10-V. If I did not have hardwired power, I would choose the Kidde 30CUD10-V. For remote notifications, I would choose between the Kidde Ring Smart Smoke + CO Alarm and the First Alert SC5, depending on which smart-home ecosystem I wanted to use.

First, Figure Out What You Are Replacing

Before ordering anything, take one of your existing alarms down and read the label on the back.

Write down:

• The manufacturer
• The model number
• The manufacture date
• Whether it is hardwired or battery-only
• Whether there is an interconnect wire
• Whether it detects smoke only or smoke and carbon monoxide

If you have a hardwired interconnected system, this is particularly important. You should not assume that an alarm from another manufacturer—or even every alarm from the same manufacturer—can simply be mixed into the existing interconnect network.

Check the replacement alarm’s compatibility documentation before buying a houseful of them.

Best Overall Hardwired Smoke and CO Alarm: Kidde 30CUA10-V

The Kidde 30CUA10-V is the conventional alarm I would start with for a new hardwired installation.

It combines smoke and carbon monoxide detection in one unit, runs from house power, includes a 10-year backup battery and provides voice alerts. It can also use the hardwired interconnect so compatible Kidde alarms throughout the house sound together.

The 10-year backup battery is especially appealing. A hardwired alarm still needs backup power when utility power is out, but there is no 9-volt battery to remember to change every year.

Voice alerts are another feature I like. Instead of receiving only a generic siren, the alarm can announce whether the warning is for fire or carbon monoxide.

I would buy it for: a hardwired home where I want combination smoke and CO protection, wired interconnection, voice alerts and no routine backup-battery changes.

Check the Kidde 30CUA10-V on Amazon

Best First Alert Hardwired Replacement: SMICO105-AC

If your house already uses compatible First Alert or BRK hardwired alarms, the First Alert SMICO105-AC may be the more natural replacement.

It is a hardwired combination smoke and CO alarm with a 10-year battery backup and wired interconnect support. First Alert also uses a quick-connect plug intended to simplify replacement in compatible installations.

This is an important point when replacing alarms: the “best” alarm on paper is not always the best replacement for the wiring already in your ceiling.

If I already had a house full of compatible First Alert or BRK alarms, I would strongly prefer staying within the approved interconnect family rather than changing brands one detector at a time.

I would buy it for: an existing compatible First Alert or BRK hardwired system where I want a modern combination alarm and 10-year backup battery.

Check the First Alert SMICO105-AC on Amazon

Best Hardwired Smoke-Only Alarm: Kidde 20SA10-V

You do not necessarily need every detector in the house to contain a carbon monoxide sensor.

If your home already has appropriate separate CO detection, the Kidde 20SA10-V gives you the same basic hardwired approach in a smoke-only alarm.

It includes a 10-year backup battery, voice alerts and hardwired interconnection with compatible Kidde alarms.

This can make sense in a larger house where combination smoke/CO alarms are installed in the locations that need CO protection while additional smoke-only alarms provide the required fire coverage elsewhere.

Follow your local fire and building requirements when deciding where smoke and CO alarms are required.

I would buy it for: additional hardwired smoke protection in a compatible Kidde system where carbon monoxide detection is already provided separately.

Check the Kidde 20SA10-V on Amazon

Best 10-Year Battery Smoke and CO Alarm: Kidde 30CUD10-V

Many houses do not have electrical wiring at every smoke-alarm location. The building I live in was built in the 1970s and originally had no hardwired power for the detectors, so I understand the problem.

If you are not opening ceilings and running new electrical wiring, the Kidde 30CUD10-V is the simplest choice in this group.

It combines smoke and CO detection with a sealed 10-year battery and voice alerts. There is no annual battery replacement and no electrical connection to install.

The tradeoff is that this model does not give you the wired interconnection of the hardwired Kidde models above.

If your alarm reaches the end of its service life, you replace the entire alarm. That may sound wasteful until you remember that smoke alarms themselves are not lifetime devices.

I learned that lesson when one of my own sealed-battery alarms started chirping and could not be fixed with a battery change. I wrote about the experience in Why Your Smoke Detector Keeps Chirping After You Change the Battery.

I would buy it for: a location without hardwired alarm power where I want a simple combination smoke/CO alarm without routine battery replacement.

Check the Kidde 30CUD10-V on Amazon

Best Smart Smoke Detector for Ring: Kidde RGCUAR-RW

The Kidde RGCUAR-RW solves a problem I complained about in the earlier version of this article: getting modern hardwired smoke and CO detection with useful wireless connectivity.

This model is hardwired, uses two AA batteries for backup and integrates directly with the Ring app. It can send notifications for smoke, carbon monoxide and low battery conditions when you are away from home. Kidde says another Ring device is not required.

That makes it particularly interesting for a vacation home, rental property or any house that sits empty for stretches of time.

A local alarm is designed to warn people inside the building. A remote notification gives you a chance to learn about a problem when nobody is there to hear it.

I would not buy a smart smoke detector solely because it is smart. The core job is still detecting smoke and CO and sounding an alarm. But if I already use Ring and want remote fire-safety notifications, this is a much more compelling product than trying to bolt a separate smart-home relay onto the interconnect wire.

I would buy it for: a hardwired home where Ring is already part of the monitoring system, especially a second home or property that is sometimes unoccupied.

Check the Kidde Ring Smart Smoke + CO Alarm on Amazon

For the rest of the second-home monitoring problem, see my guide to vacation-home remote monitoring.

Best Nest Protect Replacement: First Alert SC5

Google Nest Protect created a loyal following because it combined smoke and CO detection, voice warnings, interconnected alarms and phone notifications in a polished product.

The current First Alert SC5 is particularly interesting because First Alert designed it to work with and replace Nest Protect.

The battery model linked here is model SMCO600NV. It combines photoelectric smoke detection and electrochemical CO detection with voice and location alerts, Wi-Fi connectivity, mobile notifications and wireless interconnection with compatible alarms.

First Alert says it can work alongside Nest Protect through Google Home, which makes it the obvious model to investigate if an aging Nest Protect needs replacement.

Unlike the sealed 10-year Kidde battery model above, the SC5 battery model uses replaceable lithium batteries. Its appeal is the connected feature set rather than never having to replace a battery.

I would buy it for: someone replacing Nest Protect or building a smart smoke/CO system around Google Home and First Alert.

Check the First Alert SC5 on Amazon

Hardwired or Battery?

If the house already has hardwired smoke-alarm power, I would normally continue using it. Hardwired alarms receive normal power from the house and use their battery as backup.

If wiring is not already available, a 10-year sealed-battery alarm avoids the electrical work and eliminates routine battery changes.

Why Interconnected Smoke Alarms Matter

Interconnection means that when one alarm detects a problem, compatible alarms elsewhere in the house sound too.

That is particularly useful in a larger or multi-story home. A fire beginning in a basement, garage area or distant bedroom should not depend on someone upstairs hearing one alarm through several closed doors.

Interconnection can be wired or wireless, depending on the product.

The important word is compatible. Do not assume that every alarm with an interconnect feature can communicate with every other alarm.

What Changed With Newer Smoke Alarms?

Smoke-alarm standards continue to evolve. Current UL requirements include tests intended to improve detection of modern fires while reducing nuisance alarms caused by cooking.

That is useful because nuisance alarms create their own safety problem: people sometimes disable an alarm that goes off too often and then forget to restore it.

If I am replacing a ten-year-old alarm today, I would buy a current model from a major manufacturer rather than searching for an identical decade-old model simply because the old mounting plate looks familiar.

You can read more about the newer smoke-alarm requirements from UL Solutions.

How Many Smoke Alarms Do You Need?

The National Fire Protection Association recommends smoke alarms inside every sleeping room, outside each separate sleeping area and on every level of the home, including the basement.

Carbon-monoxide requirements depend on the home and local code, so check your state and local rules as well as the manufacturer’s instructions.

More expensive combination alarms can simplify a system, but buying one combination smoke/CO alarm does not automatically mean you have enough alarms for the entire house.

See the NFPA smoke-alarm guidance when planning locations.

How Often Should You Test a Smoke Detector?

Use the alarm’s test button at least once a month. NFPA and CPSC both recommend regular monthly testing.

A status light is not a substitute for pressing the test button. The point of the test is to verify that the alarm responds.

This is also why I would not assume a detector is healthy merely because it has not started chirping.

If you are trying to diagnose an existing detector, read what to do when a smoke detector keeps chirping after a battery change.

When Should You Replace a Smoke Alarm?

NFPA recommends replacing smoke alarms when they are 10 years old, measured from the manufacture date. An alarm that fails its test should be replaced sooner.

Combination smoke and CO alarms can have model-specific service lives, so check the label and manufacturer’s instructions.

When one old detector reaches end of life, check the dates on the rest of the alarms in the house. If they were all installed together, the others may be approaching replacement at the same time.

My Buying Decision

If I were installing a conventional hardwired system today, the Kidde 30CUA10-V would be my first choice from this group.

If the house already had a compatible First Alert/BRK interconnect network, I would choose the SMICO105-AC instead of changing ecosystems without a reason.

Without hardwired power, I like the simplicity of the Kidde 30CUD10-V.

For a property where remote notifications are important, I would choose the smart ecosystem first: Kidde with Ring or First Alert SC5 with Google Home.

Whichever model you choose, check the date on the existing alarms before ordering. A chirping detector may be telling you that one battery needs attention. It may also be telling you that the entire generation of alarms in your house is ready for replacement.

Frequently Asked Questions

What is the best smoke and carbon monoxide detector?

For a conventional hardwired home, I like the Kidde 30CUA10-V because it combines smoke and CO detection, a 10-year backup battery, voice alerts and hardwired interconnection. The best replacement can change if your house already has a compatible First Alert, BRK or Kidde interconnected system.

Should I buy separate smoke and CO detectors or a combination alarm?

Combination alarms simplify installation and reduce the number of devices on the ceiling or wall. Separate alarms can make sense where you need additional smoke detection but already have adequate carbon-monoxide coverage. Follow local requirements for both types of detection.

Are 10-year smoke detector batteries really good for 10 years?

Sealed long-life alarms are designed so the battery does not require routine replacement during the alarm’s service life. The alarm should still be tested regularly, and a unit that fails testing or reaches its specified end of life should be replaced.

Can I replace a hardwired smoke detector with any brand?

Do not assume so. Hardwired alarms may use different electrical connectors and interconnect requirements. Check the replacement model’s compatibility information before mixing alarms or changing brands.

What is the best smart smoke detector after Nest Protect?

The First Alert SC5 is specifically designed to work with and replace Google Nest Protect and supports Google Home. The Kidde Ring Smart Smoke + CO Alarm is a strong alternative for households built around Ring.

Do smart smoke alarms still work if the internet goes down?

The alarm itself is designed to provide local smoke and CO warnings independently of a phone notification. Internet connectivity is used for remote smart features, so do not treat an app alert as a replacement for properly installed local alarms.

How often should I test smoke alarms?

Test smoke alarms at least once a month using the test button. Replace an alarm that does not respond properly.

How old is too old for a smoke detector?

NFPA recommends replacing smoke alarms when they reach 10 years from the manufacture date. Check combination smoke/CO alarms for the model-specific replacement interval printed on the device or in its instructions.