Product Library / Security Systems & Alarms
Research profile · last verified 2026-07-19First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
Compatibility
| Ecosystem | Support | The catch |
|---|---|---|
| Amazon Alexa | Doesn't workVerified: does not work with this ecosystem | Not supported. First Alert's SC5 pages name only the First Alert app and Google Home, and the launch announcement names only Google. Worth flagging for anyone replacing the older Safe & Sound, where Alexa was a headline feature — that model is discontinued. |
| Google Home | WorksWorks with this ecosystem | Documented from both sides, and smoke/CO events themselves reach Google Home — not just device presence. Also relays events to and from Nest Protect alarms in the same home, which is the migration path Google points Protect owners at. |
| Apple Home | Doesn't workVerified: does not work with this ecosystem | First Alert states it plainly in its own support article: "The SC5 Smart Smoke & CO Alarm does not have native Homekit/Siri support." The same article lists the HomeKit-capable First Alert alarms as OBSOLETE models — so an Apple household replacing an Onelink is losing the integration, not carrying it over. |
| SmartThings | Doesn't workVerified: does not work with this ecosystem | First Alert's own support article states that other First Alert and Onelink alarms, excluding the Z-Wave ZCOMBO, are not compatible with SmartThings. The ZCOMBO is a different, hub-required Z-Wave product, not this one. |
| Home Assistant | Not checkedWe have not verified this yet — this is not a claim about the product | No official Home Assistant integration was confirmed either way — HA's integration index would not render to research tooling, so we cannot yet publish a definite no. An unofficial community integration polls Resideo's cloud and exposes the alarm states; that is not covered by this claim. |
? Not checked means we haven’t verified that ecosystem yet — it is a statement about our research, never a verdict on the product. A Setup Check can research it for you.
Protocols: WIFI
Subscription reality
✓ Works without a subscription: Yes.
No paid plan found for any alarm function. Free accounts are required (a First Alert account, plus a Google Account for Google Home), but nothing is behind a paywall.
Maintenance reality
- Batteries: 6× CR123A 3V lithium, replaceable (battery model); 120V AC with lithium backup (hardwire model)
- Cloud dependence: Yes — a server shutdown would degrade or brick this device
- Ten-year end-of-life signal from installation, matching the mandated sensor lifespan; 10-year limited warranty. Seven-day low-battery warning. Local alarming, the sounder, and both wireless and hardwire interconnect are device-side and survive an internet outage; push alerts, remote test/silence and Google Home all need Wi-Fi plus Resideo's cloud. First Alert's own two pages disagree on whether the hardwire model's backup battery is replaceable — recorded as unresolved rather than picked.
The catch
This is the alarm Google points Nest Protect owners toward, and it talks to Google Home and almost nothing else. The Onelink generation it replaced had genuine Apple HomeKit support; First Alert now states the SC5 does not, and SmartThings is ruled out in writing too. An Apple Home or Alexa household gets a Wi-Fi alarm that reaches the First Alert app and Google Home only.
Who it's for
Google Home households, and Nest Protect owners looking at the successor Google itself names — the two interconnect. Households on Apple Home, Alexa or SmartThings should note that all three are documented as unsupported.
Sources & method
firstalert.com/products/sc5-hardwire-smart-smoke-carbon-monoxide-alarm and .../sc5-battery-... — $129.99 MSRP both variants; SC5 wired user manual (2.4 and 5 GHz Wi-Fi, ~10-year end-of-life signal, 7-day low-battery warning, orange hardwire interconnect max 18 units) — vendor-page and manual research, verified 2026-07-19 · First Alert's own support articles, read in a rendering browser because the site is a JS SPA that returns only a loading shell to plain fetches: support.firstalert.com HomeKit article states "The SC5 Smart Smoke & CO Alarm does not have native Homekit/Siri support" and lists 1039102/1042135/1042136 under OBSOLETE MODELS; the SmartThings article states other First Alert and Onelink alarms excluding ZCOMBO "are not compatible with SmartThings". Vendor statements, not inference from absence. — vendor-page research (browser-rendered), verified 2026-07-19 · Counterparty source per 09 §3: support.google.com/googlehome/answer/16324143 documents SC5 setup in Google Home and states each device can relay a smoke or CO event to other compatible alarms in the home; corroborated on the First Alert side by firstalert.com/blogs/safety-corner/replacing-your-google-nest-protect-with-first-alert — counterparty-source research, verified 2026-07-19 · csa-iot.org certified-products search returned no First Alert or BRK entries; the only Resideo Matter certifications found were thermostats (ElitePRO/X8/X7) — registry research, verified 2026-07-19 · firstalertstore.com product records for 1039102, 1042135 and 1042136 all read "Sorry, this item has been DISCONTINUED." No dated discontinuation announcement was found, and First Alert publishes no statement on whether existing Onelink units keep working — both recorded as unknown rather than assumed. — vendor-page research, verified 2026-07-19 · resideo.com corporate newsroom publishes the First Alert / Google Nest partnership announcement — First Alert is a Resideo brand — vendor-page research, verified 2026-07-19. This is a research profile: compiled from manufacturer documentation, certification registries, and published testing — we state facts, not verdicts, and we have not physically tested this unit. How we work →
Compatibility and lifecycle information reflects the last-verified date above and can change without notice (firmware updates, cloud-service changes, discontinuations). It is provided as-is, for information — verify with the manufacturer before purchasing. Spot an error? Tell us and we'll fix it. Full terms: Terms of Service.