The First Alert SC5 Smart Smoke & Carbon Monoxide Alarm meets
the X-Sense SC07 Smoke & Carbon Monoxide Alarm
The smart flagship, a dual-sensor smoke and CO alarm chosen to replace the Nest Protect. We tested it head-to-head against the X-Sense SC07 Smoke & Carbon Monoxide Alarm across 6 key dimensions.
First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
“The smart flagship, a dual-sensor smoke and CO alarm chosen to replace the Nest Protect”
X-Sense SC07 Smoke & Carbon Monoxide Alarm
“The value standout, a combo smoke and CO alarm that won hands-on tests for under fifty dollars”
Head-to-Head Breakdown
Strengths & Weaknesses
First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
- Tom's Guide's number one smart alarm and Google's official Nest Protect successor
- Dual ionization and photoelectric sensors cover both flaming and smoldering fires
- Detects carbon monoxide and sends Wi-Fi alerts through the First Alert app
- At about $130 it is by far the most expensive pick here
- As a newly launched model it can be harder to find in stock
- The full smart feature set only matters if you want app alerts
X-Sense SC07 Smoke & Carbon Monoxide Alarm
- Bob Vila's hands-on Best Overall and a SafeWise top pick, the widest praise here
- Combines smoke and CO detection with a live CO readout on the screen
- Sealed ten-year battery means nothing to wire and no batteries to swap
- The standalone model has no Wi-Fi, app or interconnect
- It uses a single photoelectric smoke sensor rather than a dual sensor
- It cannot be hardwired into an existing alarm circuit
The Verdict
Our Bottom Line
When Google discontinued the Nest Protect in 2025, it did not just walk away from smart smoke alarms. It handed the job to First Alert, and the SC5 is the result. Tom's Guide named it the best smart alarm for Google Home, and the reasons go beyond the app. It carries both an ionization and a photoelectric sensor, the dual setup Consumer Reports recommends because ionization reacts fastest to flaming fires while photoelectric catches slow, smoldering ones. It also detects carbon monoxide, so a single unit covers the three hazards most homes worry about. Wi-Fi alerts reach your phone when you are out, and it interconnects so a warning in the basement sounds upstairs too.
First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
When Google discontinued the Nest Protect in 2025, it did not just walk away from smart smoke alarms. It handed the job to First Alert, and the SC5 is the result. Tom's Guide named it the best smart alarm for Google Home, and the reasons go beyond the app. It carries both an ionization and a photoelectric sensor, the dual setup Consumer Reports recommends because ionization reacts fastest to flaming fires while photoelectric catches slow, smoldering ones. It also detects carbon monoxide, so a single unit covers the three hazards most homes worry about. Wi-Fi alerts reach your phone when you are out, and it interconnects so a warning in the basement sounds upstairs too.
- Anyone who wants the widest hazard coverage in one alarm
- Google Home users who want Wi-Fi and app alerts
- People replacing an aging Nest Protect
X-Sense SC07 Smoke & Carbon Monoxide Alarm
The X-Sense SC07 is the alarm that keeps showing up. It placed across four of our six sources and won Bob Vila's hands-on test outright, where its synthetic smoke spray set it off in roughly ten seconds, the fastest result in that group. For under fifty dollars you get combined smoke and carbon monoxide detection, a backlit screen that shows the live CO reading in the room, and a sealed ten-year battery, so there is nothing to wire and no batteries to change for a decade. It gives up the smart features and the dual smoke sensor of the SC5, but it nails the core job for a quarter of the price.
- Anyone who wants smoke and CO protection for the lowest price
- Renters who want a battery alarm with nothing to wire
- Buyers who like the live carbon monoxide readout