Product Library / Security Systems & Alarms

First Alert SC5 Smart Smoke & Carbon Monoxide Alarm

Compiled by SmartHomeWorkflow Research · First Alert · Security Systems & Alarms · ~$130 ($129.99 on First Alert's own store, re-verified 2026-08-12 — unchanged from the recorded MSRP and never treated as a live price. ⚠ AVAILABILITY CHANGED at the same read: the hardwire SKU (FSMCO600NVACCL1 / model SMCO600NV-AC) shows as unavailable, backordered on First Alert's own page. That is a stock state on a date, NOT a discontinuation — the product is still listed, priced and described, and First Alert has said nothing about ending it.)

Compatibility

? Not checked yet means we haven’t researched 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^[4][7]

What it can do^[9]

Listed capabilities are what we could establish from vendor documentation. An ability missing here is unestablished — not necessarily absent.

Subscription reality

✓ Works without a subscription: Yes.

Vendor account required: Not established — we have not sourced this yet.

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)
• Works without the internet: Partly — some of it keeps working and some of it does not. See the detail below.^[1]
• 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.

Security updates^[10]

First Alert publishes no security-update support date for this model. That is a gap in what the manufacturer has published, not evidence either way — some makers declare a support period and some say nothing at all.

Verified absence, earned by walking the rungs rather than defaulted. Resideo publishes no security-update period for this product, on its product-security page, its vulnerability-disclosure page, or the product's own page. What Resideo does publish is more revealing than silence: its two end-of-support events were both driven by a CERTIFICATE EXPIRING rather than by a support window running out. So the practical horizon for a Resideo connected product is the life of a PKI certificate nobody publishes the expiry of, and the vendor's own precedent is that when one lapses the device stops being installable. That is a different and less predictable shape than a stated period, and it is why this absence is recorded with the precedents attached. Recheck condition: Resideo publishes end-of-support notices on honeywellhome.com; a notice naming this model converts this cell into a date.

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

Numbered sources below back the facts marked with the matching number above. 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 →

1. [1] 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
   Backs: Product identity, Price, Market availability, Required hub or bridge, Works without the internet
2. [2] 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
   Backs: SmartThings compatibility, Apple Home compatibility
3. [3] 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
   Backs: Google Home compatibility
4. [4] 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
   Backs: Protocols
5. [5] 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
   Backs: Market availability, Service status, Research status
6. [6] 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
   Backs: Product identity
7. [7] firstalert.com/products/sc5-hardwire-smart-smoke-carbon-monoxide-alarm, read 2026-08-12. Price $129.99, matching the recorded MSRP. 🔴 THE CHANGE IS AVAILABILITY, NOT PRICE: the page reports the hardwire model **unavailable / backordered**, where the 2026-07-19 read found it orderable. Recorded as a dated stock state and explicitly NOT as a lifecycle change — `soldUntil` stays `current` because the product remains listed, priced and documented, and a backorder is a supply condition rather than an end of sale. The distinction matters: reading 'out of stock' as 'discontinued' is how a catalogue manufactures a definite negative out of a temporary one (P-10). Full SKU captured for the first time: FSMCO600NVACCL1 for model SMCO600NV-AC. The Google cell is re-confirmed from the vendor's own framing — the page sells it as 'Compatible with and replaces Google's Nest® Protect Alarm' and documents interconnection with Nest Protect units — while no other ecosystem is named anywhere on it, which is why Alexa, Apple and SmartThings stay `none`. Wi-Fi is stated in the feature list. The live listing is the service-axis evidence. — vendor-page research, verified 2026-08-12
   Backs: Price, Market availability, Service status, Google Home compatibility, Protocols
8. [8] BQ-107 re-verification batch 30, 2026-08-12. Every axis re-read against First Alert's own product page. One fact moved — availability, from orderable to backordered — and it is recorded as a dated stock state with the reasoning for NOT treating it as a lifecycle change written alongside it. No integration level moved. ⚠ Stated limit: the service note's Onelink-migration history was not re-checked at source this pass; what was re-verified is that the product is still offered and still documented by its maker, which is what the service axis records. — re-verification batch, verified 2026-08-12
   Backs: Research status
9. [9] https://support.google.com/googlenest/answer/16324143 — the ecosystem's own integration documentation for this device (read 2026-08-20) — ecosystem integration document, plain fetch, verified 2026-08-20
   Backs: Capabilities
10. [10] Three Resideo first-party surfaces, all read 2026-08-20 and none carrying a support period. (1) resideo.com/us/en/support/security/ publishes no defined support duration, no end-of-support policy and no per-model timeframe. (2) The Resideo responsible-disclosure page describes its Coordinated Vulnerability Disclosure process and PSIRT investigation, and commits to no timeline for patch availability and no duration of support. (3) Resideo's two published end-of-support announcements are the informative part: the legacy Wi-Fi Water Leak Detectors ended installation support because "The security certificates used by these devices have expired" and "the certificates cannot be updated", with devices not online as of January 12, 2026 no longer installable; and the Honeywell Home Smart Security Kit ended October 31, 2024 because a certificate "was created and maintained by Honeywell" and Honeywell chose not to renew it. — vendor policy-page research (BQ-192 security-support sweep, method note 69 rungs a–c), verified 2026-08-20
    Backs: Security-update support period
11. [11] First Alert, SC5 Hardwire Smart Smoke & Carbon Monoxide Alarm product page (https://firstalert.com/products/sc5-hardwire-smart-smoke-carbon-monoxide-alarm), read 2026-09-03 through tools/lib/gated-fetch.mjs (HTTP 200). THE SURFACE SEARCHED AND THE COUNT: across the whole rendered page text, "Alexa" occurs ZERO times, as do "Apple", "HomeKit", "SmartThings" and "Home Assistant". What the page DOES name is the First Alert app — "Works with First Alert App" — and Google, in the sense of the hardware it replaces: "Compatible with and replaces Google's Nest® Protect Alarm". This is the vendor's own product surface omitting Alexa, which is the negative standard this catalogue's vocabulary sets for `integrations.alexa: none`. — vendor-page research (BQ-322 batch 5 — claim-coverage cells, first-party re-read through tools/lib/gated-fetch.mjs), verified 2026-09-03
    Backs: Amazon Alexa compatibility

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.

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