Disclosure: We may earn commissions from qualifying purchases of these smart detectors, but our 2026 rankings remain entirely independent and honest, ensuring you get only
As an Amazon Associate I earn from qualifying purchases.
A smart smoke and CO alarm does one thing a dumb one can’t: it tells you what’s happening and where when you’re not home, instead of just making noise in an empty house. Before picking one, there’s a real market shift worth knowing about — Google discontinued its own Nest Protect line in 2025 and handed the smart-alarm torch to First Alert, whose new Smart Smoke & CO Alarm is built to interconnect with any Nest Protect units you already own. That changes what “the Google ecosystem pick” actually means in 2026. This roundup covers four genuinely different picks: the current Google-ecosystem successor, a no-hub standalone option, a hardwired whole-home pick with air-quality monitoring, and the outgoing Nest Protect itself for anyone extending an existing setup.
First Alert SC5 Smart Smoke & CO Alarm: the Google Home ecosystem pick
The SC5 is First Alert’s answer to the Nest Protect gap, built specifically to work inside the Google Home app and to interconnect with any Nest Protect alarms already installed in your house — Google confirmed the two lines talk to each other so a mixed-alarm household isn’t stuck buying a full replacement set. It comes in three power configurations (10-year sealed battery, replaceable battery, and hardwired-with-battery-backup), which is more flexibility than most single-model alarms offer. First Alert’s Precision Detection Technology is aimed squarely at the most common complaint about smoke alarms in general: false alarms from cooking steam or shower humidity setting off a 3 a.m. panic. Voice alerts announce “fire” or “carbon monoxide” by name rather than a generic beep pattern, which matters for guests or kids who don’t know the alarm’s chirp codes. The honest gap: it’s a first-generation smart product from a company whose non-smart alarms have a decades-long reputation, so the app and connectivity layer doesn’t yet have the multi-year track record Nest Protect built up before Google walked away from it.
X-Sense SC07-W: the no-hub, no-subscription standalone pick
X-Sense’s case for itself is refreshingly simple: a 10-year sealed lithium battery, a built-in LCD screen that shows live CO concentration in parts-per-million (not just an alarm/no-alarm binary), and interconnection with other X-Sense alarms over RF without needing a Wi-Fi network, a hub, or an app account at all if you don’t want one. That makes it a strong fit for a rental, a cabin with spotty internet, or anyone who wants real smart-alarm behavior (dual smoke-and-CO sensing, UL 217 and UL 2034 certification, precise threshold-based CO readings) without adding another device to a smart-home app collection. Pair it with X-Sense’s optional SBS50 base station and you do get app notifications and remote monitoring, but that’s an add-on, not a requirement. The trade-off: without the base station, you lose the “notify my phone while I’m out” feature that’s the entire point of a smart alarm for a lot of buyers — this is the pick for people who specifically don’t want that dependency, not a like-for-like swap for the SC5 or Nest Protect.
Kidde Smart Smoke, CO & Air Quality Alarm: the hardwired whole-home pick
Kidde’s smart line is built for houses that already have hardwired interconnected alarms and want to upgrade the whole system at once rather than alarm-by-alarm. It requires hardwiring (with a sealed 10-year lithium backup battery for outages), connects over 2.4GHz Wi-Fi, and works with both Amazon Alexa and Google Home for voice status checks (“is the kitchen alarm okay?”). Kidde’s newer models go a step further than pure fire/CO detection by adding an indoor air quality monitor that tracks temperature, humidity, and total volatile organic compounds (TVOCs) alongside smoke and CO — genuinely useful if you’re also interested in general air quality and don’t want a separate device for it. The honest limitation: hardwiring means an electrician or comfortable DIY rewiring job if you’re not replacing a like-for-like hardwired unit, and once the sealed 10-year battery reaches end of life you replace the whole unit rather than swapping a battery, same as X-Sense and First Alert’s sealed-battery models.
Google Nest Protect (2nd Gen): still solid, but Google has stopped making it
Nest Protect earned its reputation honestly — the second-generation model’s split-spectrum sensor (an infrared photoelectric sensor paired with a second blue LED) was genuinely better than most competitors at telling apart fast-flaring fires from slow smoldering ones, and its phone-app silence/test feature meant never climbing on a chair to swat a chirping alarm. But Google confirmed in 2025 that it has stopped manufacturing new Nest Protect units, framing the move as “passing the torch” to partners like First Alert rather than continuing to compete in the category itself. Existing units already installed keep working and remain supported, and the new First Alert SC5 is specifically designed to interconnect with them — so if you already own Nest Protect alarms, adding SC5 units elsewhere in the house is the sensible path rather than trying to track down discontinued new-old-stock Nest units of uncertain manufacture date.
Comparison table
| Alarm | Power | Connectivity | Best for | Honest drawback |
|---|---|---|---|---|
| First Alert SC5 | Battery, replaceable-battery, or hardwired | Wi-Fi, Google Home app | Nest Protect households, new Google-ecosystem buyers | First-gen smart product, no long track record yet |
| X-Sense SC07-W | 10-year sealed battery | RF interconnect; Wi-Fi app optional via SBS50 | No-hub, no-subscription buyers | No phone alerts unless you add the base station |
| Kidde Smart Smoke/CO/IAQ | Hardwired + 10-year backup battery | Wi-Fi 2.4GHz, Alexa + Google Home | Whole-home hardwired upgrades, air-quality tracking | Requires hardwiring; whole unit replaced at battery end-of-life |
| Nest Protect (2nd Gen) | Battery or hardwired | Wi-Fi, Nest/Google Home app | Extending an existing Nest Protect household | Discontinued — Google has stopped making new units |
Which one should you actually buy?
If you’re starting from scratch and want the current Google-ecosystem pick with the flexibility of three power options, the First Alert SC5 is the safest default — it’s also the only one of the four explicitly designed to talk to Nest Protect units if you inherit some later. If you want dependable smoke-and-CO protection with zero app or Wi-Fi dependency, the X-Sense SC07-W’s sealed 10-year battery and RF interconnect get you there without adding another account to manage, at the cost of losing remote phone alerts unless you add the base station. If you’re upgrading a fully hardwired system and want indoor air quality data as a bonus, Kidde’s combined smoke/CO/IAQ alarm is the only one here that does all three. And if you already own Nest Protect alarms, don’t rush to replace them — they’re still supported, and First Alert’s SC5 is built to extend that setup rather than force a full swap.
FAQ
Should I replace my existing Nest Protect alarms now that Google discontinued them?
No — Google confirmed existing units keep working and remain supported. There’s no forced end-of-life date announced; the discontinuation only affects new manufacturing. Replace individual units only when they reach their own hardware end-of-life (most smoke alarms, smart or not, have a manufacturer-set replacement age around 10 years).
Do smart smoke and CO alarms need Wi-Fi to detect smoke or CO at all?
No. Core detection (the sensor itself sounding the local alarm) works without any network connection on every alarm in this roundup — Wi-Fi and an app only add remote notifications, status checks, and silencing from your phone. If your internet goes down, the alarm still protects you locally.
Can I mix brands on one interconnected alarm system?
Generally no, with one notable exception: First Alert’s SC5 is specifically built to interconnect with Nest Protect. Outside of that pairing, treat interconnection as brand-specific — X-Sense alarms interconnect with other X-Sense alarms, Kidde with other Kidde alarms, and so on. Check each brand’s compatibility list before mixing.
How long do smart smoke and CO alarms actually last before I need a new one?
Most sealed-battery smart alarms (X-Sense, Kidde’s battery backup, First Alert’s sealed option) are rated for a 10-year sensor and battery life, after which the whole unit is replaced rather than serviced — this matches the standard non-smart smoke alarm replacement interval most fire-safety authorities recommend regardless of brand.
Related: smart home automation compatible with apple homekit