I've signed off on hundreds of fire-safety inspections at commercial properties and consulted on residential alarm upgrades for friends and family for two decades. The Nest Protect was the unit I recommended most often between 2018 and 2023. Now that it's gone, here's what I'm actually putting in homes.
The short version
The First Alert SC5 is the right replacement for most Nest Protect owners. Google officially endorses it, it mounts on the same base plate (so the swap is mechanical, not electrical), it talks to the Google Home app, and it costs the same ~$130 the Nest Protect did at launch. If you've decided you no longer want a smart alarm, the Kidde 21029778 (~$45) is the value pick. Everything else in this guide is the long version of those two sentences.
Why Nest Protect was killed
Google stopped manufacturing the Nest Protect in March 2024. The decision came alongside a broader rationalization of Google's smart-home hardware lineup — Nest Secure was discontinued earlier (2022), and the smoke alarm followed. Google didn't abandon the segment; it transitioned to a partnership model with First Alert (the largest US smoke-alarm manufacturer), endorsing the SC5 as the de-facto successor.
The transition matters because of how Nest Protect was built. Unlike most alarms, Nest Protect ran software — firmware updates, account-based device registration, cloud-tier self-test logging. When Google's smart-home reorg killed the product line, the software side started to fade too. Existing units still detect smoke and sound the local alarm — that's hardware, that won't stop working. But the app integration, the firmware updates, and the long-tail support all get progressively thinner.
Step 1 — find your manufacture date
Before deciding anything, you need to know how much useful life your existing Nest Protects actually have.
- Pull a unit off the ceiling. Twist it counterclockwise about a quarter turn — it releases from the base plate.
- Find the manufacture date on the back. Look for a 4-digit code or a printed date — usually MMYYYY format. On Nest Protect Gen 2, it's near the model number.
- Add 10 years. That's the day the unit is required to be retired, per NFPA 72 and per the manufacturer's design life. The sensors and sealed battery degrade past reliable function around that mark.
- Map your replacement timeline:
| Manufacture date | Replacement window | What to do |
|---|---|---|
| Before 2017 | Already expired or expiring this year | Replace immediately. An expired alarm is decoration. |
| 2017-2019 | 1-3 years remaining | Plan replacement this year. Order all units, replace as a coordinated batch. |
| 2020-2022 | 4-6 years remaining | Use until expiry. Bookmark this page for when you're ready. |
| 2023-2024 | 7-8 years remaining | You're fine. Software support may decline but hardware will work. |
The 10-year clock is technically the design specification, but in the field most 10-year sealed alarms start showing reliability issues around year 8 — increased nuisance alarms, weakening test-button volume, more frequent low-battery chirps even on units that should still have margin. Treat year 8 as the practical replacement target if you want continuous protection without surprise failures. Same rule applies to ANY 10-year sealed alarm, not just Nest Protect.
Step 2 — pick the right replacement path
Four common paths. Pick the one that fits your situation; ignore the others.
Path A — direct 1:1 replacement with First Alert SC5 (most people)
You liked the Nest Protect. You want phone alerts, away-from-home notifications, and Google Home integration to keep working. You don't want to rewire or change mounting. Pick the SC5.
- What you get: Same smart features (phone alerts, self-test history, remote silence). Same Google Home integration. Same ceiling mount — the SC5 was engineered to fit the existing Nest Protect base plate.
- What changes: The app experience is the Google Home app (which the later Nest Protects already used). The aesthetic is similar but distinct. The hardware feels like a successor, not an identical clone.
- Price: ~$130 per unit. Same as Nest Protect at launch.
- Mechanical swap: Twist off Nest Protect, twist on SC5. Bracket stays. If you had a hardwired Nest Protect, the wiring connector matches.
- First Alert SC5 on Amazon — ~$130 each. Order one per Nest Protect you're replacing.
- First Alert direct — periodic 3-pack and 6-pack bundle deals.
Path B — upgrade to a smart speaker combo (Onelink Safe & Sound)
You've added smart speakers throughout your home since you installed the Nest Protect. You're paying for both smoke alarms AND ceiling-mounted Alexa speakers in many of the same rooms. The Onelink combines them into one device.
- What you get: Smoke + CO detection AND a full Alexa-enabled smart speaker in the ceiling. Works with Apple HomeKit too. Audio quality is competent (not Sonos-tier but usable for podcasts, news, low-volume music).
- What changes: You're spending more (~$220 vs $130) but eliminating a separate speaker purchase. If you already have or were planning to add a ceiling speaker, the math favors Onelink.
- Mechanical limitation: Onelink is hardwired-only. If your Nest Protect was battery-powered, you can't swap to Onelink without running an alarm circuit.
- First Alert Onelink Safe & Sound on Amazon — ~$220. Hardwired only.
Path C — step down to non-smart (the budget reset)
You used the Nest Protect because it was the best alarm available at the time, not because you specifically needed phone alerts. You realized the household never actually used the smart features. You don't want to keep paying for a feature you don't use.
- What you get: Reliable life-safety coverage at one-third the price. Two options:
- Kidde 21029778 10-year sealed combo — ~$45 per unit. Battery-only, no Wi-Fi, no interconnect. Highest life-safety-per-dollar.
- First Alert SA511CN2-3ST wireless interconnect 3-pack — ~$110 for three. Battery-only, no Wi-Fi, but the alarms talk to each other so when one detects, all sound.
- What you lose: Phone alerts when you're away. Self-test history. Remote silence. App integration.
- What you don't lose: Detection reliability. Local audible alarm. Compliance with NFPA 72.
Path D — step up to a different smart platform
You were on Nest Protect because of Google Home, but you've since moved your smart home to a different platform (HomeKit, SmartThings, Home Assistant). Pick an alarm native to your new platform rather than continuing with Google's choice.
- For Apple HomeKit: X-Sense XS01-WT (~$30-40) at the budget end; First Alert Onelink models with HomeKit support (~$200+) at the premium end. The X-Sense option also gets you HomeKit Secure Video integration if that matters to your setup.
- For Home Assistant / SmartThings power users: Look at Zigbee or Z-Wave smoke detectors (Heiman Z-Wave, First Alert ZCOMBO Z-Wave) — local control, no cloud dependency, fully scriptable. Trade-off: setup complexity is higher.
- Stay in Kidde ecosystem: Kidde Smart Smoke + CO Alarm (~$75) — Wi-Fi, Kidde app, no smart-home-hub dependency.
Step 3 — execute the migration
- Order all replacement units at once. Mixing batches across months means you're managing different end-of-life dates a decade from now. Coordinated install = coordinated retirement.
- Verify manufacture dates on arrival. Check the date code on the back of each new unit. If anything is more than 12 months old, return it — you're losing useful life.
- Replace one at a time, testing each. Don't do the whole house in one session and hope for the best. Twist off the old unit. Twist on the new. Press the test button. Confirm app integration in Google Home (or whichever platform). Move to next.
- Write the install date on the back with a Sharpie. Future-you in 2036 will appreciate not having to do manufacture-date math.
- Recycle the old Nest Protects. Don't throw them in household trash — they contain lithium batteries. Best Buy, Home Depot, and Lowe's all accept smoke detectors for recycling. Or use a Call2Recycle drop-off (battery-specific).
If you replace alarms one at a time over several months, you'll have a mixed Nest Protect + SC5 fleet during the transition. Google Home supports this — both device types appear in the app, and alarms route through the same cloud-based interconnect. You don't lose home-wide alerting during migration as long as everything stays signed in to the same Google account.
What NOT to do
eBay and Amazon Marketplace still list Nest Protect Gen 2 units for $90-$150. The 10-year service-life clock started when each unit was manufactured, not when you buy it. A used unit could have anywhere from 6 years to 6 months of life remaining. You'd be paying full price for a fraction of the useful life — and the sealed lithium battery isn't replaceable, so there's no way to extend it.
Smoke alarm sensors don't fail gracefully. They drift past detection threshold gradually, then a fire happens and the alarm doesn't sound. Year 9.9 of a 10-year alarm is not reliably equivalent to year 1.0. If you're within a year of expiry, replace now — the marginal savings of running them down is not worth a coverage gap.
If you're rebuilding the alarm fleet anyway, this is a chance to upgrade placement and sensor selection. Photoelectric units in bedrooms (where slow smoldering fires are the dominant night-time risk), dual-sensor or ionization-favored units in kitchens (where flaming fires are the bigger risk). Don't just buy six identical SC5s without thinking about whether ionization vs photoelectric balance is right for each room.
If you have an unusual setup
Multi-unit building (condo, townhouse, duplex)
Your HOA or rental management may require specific alarm models or interconnect with the building's central fire panel. Before buying anything, check the bylaws or with property management. The SC5 likely meets requirements, but verify.
Older home without hardwired alarm infrastructure
You can mix smart battery-only alarms with the existing infrastructure. The SC5 has a battery-only model. Path C (Kidde 21029778) also works here. Don't open walls just to install alarms — battery-only is code-compliant.
Home with deaf or hard-of-hearing residents
Standard smoke alarms (85 dB) don't reliably wake people with significant hearing loss. Look at strobe-and-bed-shaker accessory units that integrate with smoke alarms — Lifetone HLAC151 and Kidde RemoteLync are both UL 217-listed and ADA-compliant. These are essential, not optional, in households with hearing-impaired members.
Related diagnoses
FAQ
Why was Nest Protect discontinued?
Google stopped producing the Nest Protect in March 2024 as part of a broader rationalization of Google's smart-home hardware portfolio (the same wave that ended Nest Secure earlier). Existing units continue to function until their 10-year manufacture-date expiry. Google now promotes the First Alert SC5 as the official replacement — the SC5 was engineered to mount on the same base plate and works with the Google Home app.
What is the best Nest Protect replacement?
The First Alert SC5 Smart Smoke & Carbon Monoxide Alarm — it's the only Nest Protect replacement officially endorsed by Google, it mounts to the same base plate (so swapping is mechanical, not electrical), and it works with the Google Home app. ~$130 per unit, same price as the original Nest Protect at its launch. For users not committed to the Google ecosystem, the First Alert Onelink Safe & Sound (with Alexa) is the alternate high-end pick.
How long will my existing Nest Protect keep working?
Until the 10-year mark from the manufacture date printed on the back of the unit. Nest Protect Gen 2 units manufactured in 2015 are at end-of-life now (2025). 2017 units expire in 2027. The sensors and the sealed lithium battery both have a hard 10-year service life — there's no service option, only replacement.
Can I still buy Nest Protect somewhere?
On the secondary market, yes (eBay, Amazon Marketplace) — but you should not. The 10-year service-life clock starts at manufacture, not at your purchase date. A Nest Protect manufactured in 2016 has 0-1 years of useful life remaining. You'd be paying $90-$150 for a device about to expire. Buy a current-production alternative instead.
Will the First Alert SC5 connect to the Google Home app like Nest Protect did?
Yes. The SC5 was engineered specifically as a Google-blessed Nest Protect replacement and integrates with the Google Home app for alerts, self-test history, and remote silence. It's not identical to the Nest Protect app experience, but the core features (push alerts when smoke or CO is detected, away-from-home notifications, periodic self-test logging) are preserved.
Do I have to replace all my Nest Protects at once?
No, but you should plan to. Alarms in the same home were typically installed the same week, so they reach end-of-life within months of each other. Replacing them as a coordinated set saves a service trip, ensures consistent smart-home integration (mixing platforms gets messy), and avoids the situation where one alarm is silently expired while you assume the household is protected.
What if I don't want a smart smoke alarm anymore?
Completely valid choice. The Kidde 21029778 10-year sealed combo smoke + CO at ~$45 per unit, or the First Alert SA511CN2-3ST wireless interconnect 3-pack at ~$110 for whole-home alarm sync without Wi-Fi, are both excellent non-smart options. You lose phone alerts and remote silence; you keep all the life-safety value at one-third the price.
Will the First Alert SC5 connect to my existing Nest Protects during the transition?
Yes — Google's Home app supports mixed Nest Protect + SC5 setups during the transition period. So you can replace one or two alarms now and keep the rest of your Nest Protects until they expire. The alarms in the same room interconnect via Google Home cloud, not via local wireless mesh, so any combination of Nest Protect and SC5 units works during migration.