First Alert SC5 Review

What you are actually buying. The SC5 is a smart combination alarm: photoelectric smoke sensing in one chamber, an electrochemical carbon monoxide cell in another, 85 dB at 10 feet, voice announcement rather than tone alone, Wi-Fi, wireless interconnect, and a ten-year limited warranty. First Alert publishes it as model SMCO600NV in a 5.75 in disc 1.6 in deep. It exists in two versions — the battery unit reviewed here and a hardwire version for a position that already has alarm wiring in it.

The Nest angle is the real reason it exists. Google stopped producing the Nest Protect and promotes the SC5 as the replacement, and the two share a mounting bracket: an owner can twist out a Nest unit and mount an SC5 in its place without touching the ceiling. More usefully, the SC5 interconnects wirelessly with compatible First Alert and Nest Protect units, which means a house full of Nest alarms can be converted a unit at a time as each one reaches its date instead of all at once. If that is your situation, this is the alarm, and Nest Protect vs First Alert SC5 works through the changeover step by step.

The battery design is the thing nobody mentions. Current combination alarms overwhelmingly ship with a sealed ten-year lithium battery: nothing to buy, nothing to change, and no low-battery chirp until the unit is genuinely finished. The SC5 instead takes six user-replaceable 3V CR123A lithium cells. That is a deliberate engineering choice — the radio and the voice announcements draw real current — but it has consequences a buyer should price in. CR123A is a camera-and-flashlight battery, not a supermarket AA. Six of them is a non-trivial purchase. And a replaceable battery reintroduces the failure mode that sealed batteries were invented to remove: the chirp at 3 am, the cell pulled out to stop it, the alarm that is then dead for a year. If the household history includes a single removed battery, read smoke detector chirping and then buy a sealed unit instead.

The paperwork gap. First Alert's specification table for the SC5 reads "Conforms to UL 217 10th Edition Standard" and lists no UL 2034 number. UL 217 is the smoke-alarm standard, and the 10th edition is the current one — the edition that added a cooking-nuisance test, which is a genuinely meaningful upgrade. UL 2034 is the separate standard for residential carbon monoxide alarms, and it is the one that fixes the thresholds a CO alarm must respond at. We could not verify a published UL 2034 listing for the SC5 at the time of writing. That is not proof it lacks one; manufacturers' spec tables are often incomplete. But on a premium combination alarm it is a question worth asking the seller before you buy, because the CO half of a combination alarm is the half you can never test with a real hazard. UL 217 certification explained covers what each standard actually tests.

Detection, honestly. Photoelectric sensing is the right primary technology for a home — it responds faster to the smoldering fires that kill people in their sleep, and it is far less nuisance-prone near a kitchen. What the SC5 does not have is an ionization chamber, which responds faster to fast flaming fires. A single photoelectric alarm is not a weakness so much as a trade, and the standard answer is coverage rather than cleverness: more alarms, in more rooms, interconnected. Ionization vs photoelectric sets out which fires each one wins.

Where the SC5 is genuinely the correct purchase: a house with Nest Protect units coming up on their ten-year dates; one landing or hallway position where a phone notification has real value because the house is often empty; a household that wants a spoken location rather than a tone. Where it is not: every ceiling in the house. Smart alarms are worth having at the positions where the notification changes what you would do, and ordinary sealed-battery alarms are worth having everywhere else. Smart vs regular smoke detectors is the page for that decision.

This is the comparison that decides the SC5 for most buyers, so it belongs in the review rather than in a footnote. The X-Sense SC07-W does the detection job to the same shape — photoelectric smoke, electrochemical CO, wireless interconnect across the house — with a sealed ten-year battery and both listings published, for a small fraction of the per-position cost.

What it cannot do is reach your phone. If the house is empty for ten hours a day, or if there is an elderly relative in it, or if a rental needs to notify a manager, that is a real gap and the SC5 closes it. If the house is occupied most of the time and the point of the alarm is to wake people in it, the notification is a convenience and the sealed battery is the feature.

Our standing recommendation for a whole house is the boring one: sealed-battery interconnected alarms everywhere, and a smart unit only at the positions where a notification would change what you do. Best smart smoke detectors ranks the smart tier, and best combination smoke and CO alarms covers the rest of the ceiling.