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Heating season is when carbon monoxide and home fires peak, so October is the right time to check your alarms. If you relied on Google's Nest Protect, there is extra news: Google has discontinued it and partnered with First Alert. We compared four combination smoke and CO alarms on Amazon, from a simple battery unit to a smart alarm that sends alerts to your phone.
Our Picks at a Glance
- Best Overall: First Alert Battery Smoke and CO Combination Alarm
- Best Hardwired: Kidde Hardwired Smoke and CO Detector with Voice Alerts
- Best Value Multi-Pack: X-Sense SC06 Smoke and CO Alarm, 5-Pack
- Best Smart Alarm (Nest Protect Replacement): First Alert SC5 Smart Smoke and CO Alarm
1. First Alert Battery Smoke and CO Combination Alarm — Best Overall
A straightforward 2-in-1 battery alarm from the best-known alarm brand, with newer sensing that reduces cooking nuisance alarms.
- Smoke and carbon monoxide detection in one unit
- Precision Detection sensing built to newer standards that reduce cooking false alarms
- End-of-life warning when it is time to replace the alarm
- Battery operated: no wiring needed
- Test/silence button; Amazon rating 4.5/5 (1,200+ ratings)
Pros: easy to install anywhere, trusted brand, fewer false alarms from cooking.
Cons: not smart and not interconnected; batteries need checking.
Best for: adding protection to bedrooms, hallways and rentals quickly.
2. Kidde Hardwired Smoke and CO Detector with Voice Alerts — Best Hardwired
A hardwired combination alarm with a 10-year battery backup that tells you out loud which danger it has detected.
- Hardwired 120V with a sealed 10-year backup battery
- Voice alerts: "Fire!" for smoke, "Warning! Carbon monoxide!" for CO
- Sensing designed to reduce cooking false alarms
- Meets UL 217 9th Edition and UL 2034
- Interconnect so all alarms sound together; Amazon rating 4.3/5 (400+ ratings)
Pros: no battery changes for a decade, clear voice alerts, interconnects with compatible alarms.
Cons: needs existing alarm wiring; check connector compatibility with your old alarms.
Best for: replacing old hardwired alarms in houses.
3. X-Sense SC06 Smoke and CO Alarm, 5-Pack — Best Value Multi-Pack
A five-pack of combination alarms with an LCD screen that shows the current carbon monoxide level, enough to cover a whole home.
- Photoelectric smoke sensor and electrochemical CO sensor
- LCD display shows real-time CO readings and battery level
- Meets UL 217 and UL 2034 (ETL listed)
- No wiring: mounts on any wall or ceiling
- Five alarms in one pack; Amazon rating 4.5/5 (400+ ratings)
Pros: covers a whole house at once, CO level on screen, easy installation.
Cons: not interconnected; lesser-known brand than First Alert or Kidde.
Best for: outfitting a whole home or several rooms at once.
4. First Alert SC5 Smart Smoke and CO Alarm — Best Smart Alarm (Nest Protect Replacement)
First Alert's smart alarm, built to work with existing Nest Protect alarms, sends alerts to your phone when you are away.
- Smoke and CO detection with phone alerts through the First Alert app
- Compatible with Google Nest Protect alarms
- Interconnect: when one alarm sounds, all compatible alarms sound
- Voice alerts with a heads-up warning that names the danger and room
- Low-battery notifications to your phone; Amazon rating 3.0/5 (600+ ratings)
Pros: phone alerts when you are away, works with existing Nest Protect units, voice and location alerts.
Cons: low average rating so far, with complaints about app setup; check recent reviews before buying.
Best for: Nest Protect owners and anyone who wants remote alerts.
Side-by-Side Comparison
| First Alert Combo | Kidde Hardwired | X-Sense SC06 | First Alert SC5 | |
|---|---|---|---|---|
| Power | Battery | Hardwired + 10-yr battery | Battery | Battery |
| Smart phone alerts | No | No | No | Yes |
| Voice alerts | Not listed | Yes | No | Yes |
| Interconnect | No | Yes | No | Yes |
| Extra | Cooking-resistant sensing | UL 217 9th Ed. | CO level display | Works with Nest Protect |
| Amazon rating | 4.5 (1,200+) | 4.3 (400+) | 4.5 (400+) | 3.0 (600+) |
From the Amazon listings and manufacturers' websites, checked October 2026. Amazon ratings change daily. Prices change often, so we do not list them here.
What to Look For
- Smoke and CO in one: combination alarms protect against both dangers with fewer devices.
- Newer standards: look for UL 217 9th Edition, which aims to reduce cooking false alarms.
- Interconnect: when one alarm sounds, all sound, which matters in multi-story homes.
- Sealed 10-year battery or hardwired: no more late-night low-battery chirps.
- Smart alerts: useful if you travel or have a rental, but only as an extra to a working local alarm.
Heating Season Safety Checklist
- Test every alarm once a month.
- Check the end-of-life dates printed on the back.
- Have your furnace serviced before winter.
- Keep space heaters at least three feet from anything that can burn.
- Never run a generator or grill indoors or in a garage.
Complete your home safety setup: pair your alarms with indoor security cameras and a DIY home security system. Using a space heater? Read our guide to the best space heaters and their safety features.
How we choose: we have not tested these products ourselves. Our picks are based on manufacturer specifications, the Amazon listings and recurring themes in buyer reviews, checked in October 2026. We favor products with strong ratings from large numbers of buyers and say where a product falls short.
FAQ
Do I need a carbon monoxide detector?
If your home has any fuel-burning appliance (a gas furnace, water heater, stove, fireplace) or an attached garage, yes. Carbon monoxide has no smell or color, and winter heating season is when most CO incidents happen. Many US states require CO alarms by law.
Where should smoke and CO alarms go?
Install a smoke alarm inside each bedroom, outside each sleeping area and on every level of the home, including the basement. Put CO alarms outside sleeping areas and on each level. Follow the manufacturer's placement guide and local codes.
What happened to Nest Protect?
Google discontinued the Nest Protect smoke and CO alarm and partnered with First Alert. Existing Nest Protect alarms keep working until their end-of-life date; First Alert's smart SC5 alarm is designed to work alongside them.
How often should I replace smoke alarms?
Replace smoke alarms every 10 years, and CO alarms according to the end-of-life date on the unit, often 7 to 10 years. Many alarms now chirp or speak to warn you when they reach end of life.
Battery or hardwired?
Hardwired alarms with battery backup are standard in newer homes and can be interconnected so all of them sound together. Battery alarms are easy to add anywhere, and sealed 10-year batteries remove the annual battery change.
Affiliate Disclosure: As an Amazon Associate, I earn from qualifying purchases. This means if you click on a link and make a purchase, I may receive a small commission at no extra cost to you. Product details and ratings on Amazon change often, so check the current listing before you buy.