Best smoke detector: the maker sheets sort them by sensor, battery and interconnect, and NFPA's placement rule matters more than any of it
Kidde 20SD10 for battery-only homes, 20SA10 for hardwired, both listed to UL 217:2024 Ed.10; First Alert dual sensor runner-up; NFPA placement and the 10-year rule.
- Verified
- Updated
- 12 min read
- 25 sources
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OwnerSpec compares published manufacturer specifications, certification listings and sourced technical documents. Unless a page explicitly states otherwise, OwnerSpec has not laboratory-tested or used the products it compares. Editorial policy
Short answer
For a home with no alarm wiring, the pick is the Kidde 20SD10: Kidde’s page prints a photoelectric sensor, a sealed 10-year battery, 85 dB at 10 ft and a 10-year limited warranty, and Kidde’s Intertek certificate lists it under UL 217:2024 Ed.10. Its one flaw is printed in the same spec table: interconnects, No. For a home with alarm wiring, the pick is the Kidde 20SA10, the model Kidde names to replace the i12010S: photoelectric, 120 V hardwired, a 10-year non-replaceable lithium backup and hardwire interconnect with compatible Kidde alarms. The runner-up is the First Alert SM310, the only sealed 10-year alarm here whose maker prints both photoelectric and ionization sensing. Skip all of them until the placement count is done: NFPA’s tip sheet puts a smoke alarm inside every sleeping room, outside each separate sleeping area and on every level, and says to replace every alarm at 10 years. The date on the back decides more than the model on the front.
The picks
No alarm wiring and never wants to change a battery
Kidde 20SD10 (photoelectric, sealed 10-year battery)
Kidde page and guide: photoelectric, sealed 10-year battery, 85 dB at 10 ft, replace-by date 10 years from first power, interconnects: No, 10-year limited warranty; Intertek certificate lists it under UL 217:2024 Ed.10
Has alarm wiring and wants all alarms to sound together
Kidde 20SA10 (hardwired, sealed 10-year lithium backup)
Kidde page: photoelectric, 120 V hardwired, 10-year non-replaceable lithium backup, hardwire interconnect with compatible Kidde alarms, UL 217-2024 Edition 10, 10-year limited warranty; Kidde names it as the replacement for the i12010S
Has alarm wiring and prefers a backup battery it can swap
Kidde 20SAR (hardwired, AA battery backup)
Intertek certificate: listed under UL 217:2024 Ed.10 with the 20SA10; the Amazon title prints hardwired with AA battery backup; Kidde's own page and user guide were not readable this session, so interconnect count and warranty are not claimed here
Wants ionization and photoelectric in one battery alarm
First Alert SM310 (dual sensor, sealed 10-year battery)
First Alert page: photoelectric plus ionization, 10-year sealed lithium non-replaceable battery, 85 dB, replaces the SA3210, 10-year limited warranty; no UL edition and no interconnect printed on the page
Wants the lowest outlay and accepts fewer printed specs
X-Sense SD2J0AX (sealed 10-year battery, 1-pack)
X-Sense page: ETL certified, meets UL 217, 10-year sealed battery; sensor type, edition, interconnect and warranty are not printed consistently, so this page does not claim them
Replacing one failed unit in an existing i4618 chain
Kidde i4618AC (hardwired ionization, 9V backup)
Kidde data sheet: ionization, 120 VAC with 9V backup, 85 dB at 10 ft, interconnects up to 24 devices (18 initiating), UL Listed, 5-year limited warranty
Replaces a Nest Protect or wants app alerts
First Alert SC5 Battery smart smoke + CO alarm (SMCO600NV)
First Alert page: photoelectric smoke plus electrochemical CO, 6 replaceable CR123A batteries, wireless interconnect, Wi-Fi, voice alerts, 85 dB at 10 ft, conforms to UL 217 10th Edition, 10-year limited warranty
Has alarm wiring and wants the smart features
First Alert SC5 Hardwire smart smoke + CO alarm (SMCO600NV-AC)
First Alert page: hardwired interconnect, 3V lithium backup, Wi-Fi, voice alerts, conforms to UL 217 10th Edition, 10-year limited warranty
If the alarm on your ceiling is older than 10 years, this comparison is the wrong page until it is off the wall: NFPA says replace it first, and if it is chirping, the chirping guide sorts a low battery from end of life before you spend anything.
How was this shortlist built?
Every figure here is a manufacturer-published specification or a line from NFPA, USFA, UL or BRK, read on 2026-10-04 from the document named beside it. Nothing was exposed to smoke or timed by this site, and each listing was confirmed in stock the same day.
Units were compared on sensor type, power source, interconnect, voice and app features, the UL 217 edition the maker prints and the warranty. An edition number appears only where the maker prints it, and the makers do not all print the same one.
Four named candidates are absent on purpose. Kidde’s pages say the P4010ACS and P4010ACS-W are discontinued and point to the 20SA10 family; Kidde’s i12010S page says the model is to be replaced with the 20SA10; First Alert’s SA511CN2-3ST page shows it as discontinued with the SM500V as successor. No Google Nest Protect is picked: Google’s support page sets its 10-year expiry and names First Alert’s smart alarm as the compatible replacement.
Which sensor type do NFPA and USFA point to?
Neither names a winner. USFA’s page lists the choice as both ionization and photoelectric alarms, or dual-sensor alarms. NFPA’s smoke alarm page, read in full, carries no sentence on sensor type at all.
| Sensor | What the maker sheet says | Who prints it |
|---|---|---|
| Ionization | “may detect invisible fire particles (associated with flaming fires) sooner than photoelectric alarms” | Kidde i12010S and i4618 data sheets |
| Photoelectric | “may detect visible particles (associated with smoldering fires) sooner than ionization alarms” | Kidde i12010S and i4618 data sheets |
| Dual sensor | “Leading authorities recommend that both ionization and photoelectric smoke alarms be installed” | Kidde data sheets; First Alert’s SC5 page says “for maximum protection, use both” |
What did UL 217 8th edition change, and which edition do makers print?
UL 217 is the UL standard for smoke alarms. UL’s release says the 8th edition is effective for alarms being tested as of June 30 and that a cooking nuisance test was created. BRK’s notice gives the full date, June 30, 2024, says it applies to the date of manufacture, and says alarms made before it may still be sold and installed under local code.
UL’s Code Authority page describes the 8th edition test as one that exposes alarms to smoke from cooking scenarios, with smoldering and flaming polyurethane foam tests also required, and says the 9th edition adds a go/no-go flaming polyurethane test after the cooking test. Pass criteria are not printed on any page opened for this review, so none are claimed.
| What is printed | Source |
|---|---|
| Kidde 20SD10, 20SA10, 20SAR, 20SDR: “Smoke Alarms [UL 217:2024 Ed.10]” | Intertek Authorization to Mark, issued 4 September 2025 |
| Kidde 20SA10: “UL 217-2024 Edition 10” | Kidde 20SA10 product page |
| First Alert SM210V and SC5: “Conforms to UL 217 10th Edition Standard” | First Alert product pages |
| First Alert SC5: “meets the UL 217 9th Edition” | First Alert store news article, older than the product page |
| First Alert SM310: no edition printed | First Alert product page |
| X-Sense SD2J0AX: “ETL Certified – Meets UL 217 Standard”, no edition | X-Sense product page |
Where a maker’s news article and product page disagree, this page takes the product page.
How do the alarms compare on paper?
| Model | Sensor | Power | Interconnect | Voice or app | Standard printed | Warranty |
|---|---|---|---|---|---|---|
| Kidde 20SD10 | Photoelectric | Sealed 10-year battery | No | No | UL 217:2024 Ed.10 (Intertek) | 10 years |
| Kidde 20SA10 | Photoelectric | 120 V hardwired, 10-year lithium backup | Hardwire, compatible Kidde alarms | No | UL 217-2024 Edition 10 | 10 years |
| Kidde 20SAR | Not read on a maker page | Hardwired, AA backup (listing title) | Not read on a maker page | Not read | UL 217:2024 Ed.10 (Intertek) | Not read |
| First Alert SM310 | Photoelectric and ionization | Sealed 10-year lithium | Not printed | No | Not printed | 10 years |
| X-Sense SD2J0AX | Not printed consistently | Sealed 10-year battery | Not printed consistently | No | ETL, UL 217 | Not found |
| Kidde i4618AC | Ionization | 120 VAC, 9V backup | Up to 24 devices (18 initiating) | No | UL Listed | 5 years |
| First Alert SC5 Battery | Photoelectric plus CO | 6 replaceable CR123A | Wireless | Voice, Wi-Fi app | UL 217 10th Edition | 10 years |
| First Alert SC5 Hardwire | Photoelectric plus CO | Hardwired, 3V lithium backup | Hardwired | Voice, Wi-Fi app | UL 217 10th Edition | 10 years |
Interconnect is brand-locked. Kidde’s support page says its alarms are listed only with the compatible Kidde models named in each user guide, that a mixed-brand chain has not been tested as a complete system and may not meet NFPA 72 or local code, and that Kidde may be unable to honor warranty claims on a mixed-brand system.
Where do smoke alarms go, and when do they come down?
| Rule | NFPA tip sheet | USFA page | Kidde 20SD10 guide |
|---|---|---|---|
| Where | Inside every sleeping room, outside each separate sleeping area, on every level | Inside and outside each bedroom and sleeping area, on every level | Every bedroom, each sleeping area on every level |
| Interconnect | Connected so when one sounds, they all sound | Interconnected so when one sounds, they all sound | Not in the extract read |
| Distance from cooking | At least 10 feet (3 meters) from the stove | Not stated | Not within 6 ft of cooking appliances |
| Test | At least once a month | Every month | Not in the extract read |
| Replace | All alarms when they are 10 years old | 10 years from the manufacture date | Replace-by date 10 years from first power |
NFPA’s sheet adds that roughly 3 out of 5 fire deaths happen in homes with no smoke alarms or no working smoke alarms. This page adds nothing to that sentence.
New York is the one state law opened for this review: the Department of State says that from April 1, 2019 every new or replacement smoke detector sold there must be powered by a sealed, non-removable battery with a minimum 10-year life or be hard-wired. Google’s Nest page adds that California and New York allow an alarm with low-power radio interconnect to skip the sealed battery, which is why replaceable-battery wireless alarms are still sold there.
Kidde 20SD10: buy it or skip it?
Buy it for a bedroom in a home without alarm wiring. Kidde’s page prints a photoelectric sensor, a sealed 10-year battery, 85 dB at 10 ft, LED status lights and a 10-year limited warranty; the user guide sets the replace-by date 10 years from first power and says to replace the unit within 7 days of its end-of-life signal.
The flaw is in Kidde’s own spec table: interconnects, No. Five of these on three floors are five alarms that sound alone. Kidde’s guides also say ionization may catch a flaming fire sooner, so a photoelectric-only house leans on one sensor type.
Skip it if the house already has a hardwired chain: a battery alarm cannot join it, and the 20SA10 below can.
Kidde 20SA10 and 20SAR: buy them or skip them?
Buy the Kidde 20SA10 when the old i12010S or P4010ACS comes down. Kidde’s page prints photoelectric sensing, 120 V hardwired power, a 10-year non-replaceable lithium backup, hardwire interconnect with compatible Kidde alarms, UL 217-2024 Edition 10 and a 10-year limited warranty, and Kidde’s i12010S page names it as the replacement.
Buy the Kidde 20SAR if you would rather swap an AA backup than replace the whole unit when a battery fails. It sits on the same Intertek certificate under UL 217:2024 Ed.10. The flaw: Kidde’s 20SAR page and user guide were not readable this session, so its interconnect count and warranty are not claimed here.
Skip both if the existing chain is First Alert or BRK: Kidde’s support page says a mixed-brand chain is untested as a system. The hardwired replacement by brand page matches the old model to its own maker’s successor.
First Alert SM310 and X-Sense SD2J0AX: buy them or skip them?
Buy the First Alert SM310 if you want both sensor types in a battery alarm. First Alert’s page prints photoelectric plus ionization, a 10-year sealed lithium non-replaceable battery, 85 dB and a 10-year limited warranty, and says it replaces the SA3210.
The flaw is what the page leaves out: no UL 217 edition and no interconnect line. The listing title also omits the model number, so match the dual-sensor wording on the box.
Buy the X-Sense SD2J0AX for the lowest outlay. X-Sense’s page prints ETL certified, meets UL 217 and a 10-year sealed battery.
Skip the X-Sense if a printed spec matters to you: its page does not print an edition, states interconnect inconsistently, and no warranty length was found.
Kidde i4618AC and First Alert SC5: buy them or skip them?
Buy the Kidde i4618AC only to replace one failed unit in an existing i4618 chain. Kidde’s data sheet prints ionization sensing, 120 VAC with a 9V backup, 85 dB at 10 ft, interconnect of up to 24 devices with 18 initiating, and a 5-year limited warranty.
The flaw is the 9V: USFA says to replace 9-volt alarm batteries at least once a year, and the warranty is half the 20SA10’s.
Buy the First Alert SC5 Battery if you are replacing a Nest Protect or want a phone alert. First Alert’s page prints photoelectric smoke plus electrochemical CO sensing, six replaceable CR123A batteries, wireless interconnect, Wi-Fi, voice alerts, UL 217 10th Edition and a 10-year limited warranty; the SC5 Hardwire is the same alarm on 120 V with a 3V lithium backup.
Skip the SC5 if you only need smoke cover: it is a combination alarm, and the CO detector review is where its CO side is judged.
Count rooms and levels before you buy
Do not order until you have three numbers: bedrooms, separate sleeping areas and levels. NFPA’s sheet wants an alarm for each, so a three-bedroom two-storey house is five alarms minimum. Then check the ceiling: alarm wiring means 20SA10s, no wiring means 20SD10s or an SM310, and a mixed answer means a wireless chain on one brand. Write the install date on each unit; the 10-year clock starts there.
What goes wrong?
The chirp gets a new battery instead of a new alarm. Kidde’s 20SD10 guide says the unit beeps to signal end of life 10 years after it is powered, and a sealed alarm has no battery to change. The chirping guide separates the two signals; on a combination unit the CO beeping guide covers the other half.
The new alarm will not join the chain. Kidde’s support page says a model not listed in the user guide has not been evaluated for interconnection and should not be used in the chain. Match the brand and the listed models, not the wire colours.
The kitchen alarm comes down after a burnt dinner. BRK’s notice says NFPA names nuisance alarms as a leading reason alarms are disconnected, which is what the 8th edition cooking test exists to reduce. NFPA’s sheet says keep the alarm at least 10 feet from the stove.
Frequently asked questions
Photoelectric or ionization: which smoke detector should I buy?
Kidde's data sheets say ionization alarms may detect invisible particles from flaming fires sooner and photoelectric alarms may detect visible particles from smoldering fires sooner, and that leading authorities recommend both be installed. USFA's page lists both types, or a dual-sensor alarm, as the choice. First Alert's SM310 is the dual-sensor battery alarm on this page.
How many smoke alarms does a house need, and where do they go?
NFPA's tip sheet says smoke alarms should be installed inside every sleeping room, outside each separate sleeping area and on every level of the home, connected so that when one sounds they all sound, and at least 10 feet from the stove. USFA's page words it as inside and outside each bedroom and on every level. A three-bedroom two-storey house therefore needs at least five.
Do smoke detectors expire after 10 years?
NFPA's tip sheet says to replace all smoke alarms when they are 10 years old, and USFA's page counts the 10 years from the manufacture date on the back. Kidde's 20SD10 guide puts its replace-by date 10 years from first power and says to replace the unit within 7 days of its end-of-life signal. A new battery does not reset that clock.
What is the UL 217 8th edition cooking nuisance requirement?
UL's release says the 8th edition of UL 217 is effective for alarms being tested as of June 30 and that a cooking nuisance test was created; BRK's notice gives the date as June 30, 2024, applied to the date of manufacture, with earlier alarms still sold and installed under local code. Makers now print later editions: Kidde's certificate and First Alert's SC5 page say the 10th.
Can I still buy a Google Nest Protect?
Google's support page says the 2nd gen Nest Protect must be replaced after 10 years from its date of manufacture and that Google partnered with First Alert to offer its Smart Smoke & Carbon Monoxide Alarm as a compatible replacement. That page does not say the word discontinued, so this page does not either; it lists the First Alert SC5 instead of a Nest Protect.
Fact sheet and how to cite this page
- Answer
- Without alarm wiring the pick is the Kidde 20SD10: photoelectric, sealed 10-year battery, 85 dB, listed under UL 217:2024 Ed.10 on Kidde’s Intertek certificate, 10-year warranty, but no interconnect. With wiring it is the Kidde 20SA10, the model Kidde names to replace the i12010S. NFPA’s tip sheet puts an alarm in every sleeping room, outside each sleeping area and on every level, replaced at 10 years.
- Comparison basis
- Manufacturer product pages, data sheets, user guides and Kidde’s Intertek Authorization to Mark for the Kidde 20SD10, 20SA10, 20SAR, i12010S, i4618 and P4010ACS, First Alert’s SM310, SM210V, SA511CN2-3ST and SC5 pages, X-Sense’s SD2J0AX page and Google’s Nest Protect support pages, compared on sensor type, power source, interconnect, voice and app features, the UL 217 edition printed and the warranty; placement and replacement from NFPA’s tip sheet, NFPA’s smoke alarm page and USFA’s page; the UL 217 8th edition date from BRK’s notice and UL’s release.
- Assumptions
- The reader lives in the US; a home with alarm wiring already has a hardwired chain on one brand, and a home without it is buying battery alarms
- The standard and edition printed by each maker is taken as printed; this page did not look up UL Product iQ, and the makers do not all print the same edition
- A sealed 10-year alarm is replaced, not re-batteried, when it signals end of life
- Method
- OwnerSpec compared manufacturer-published specifications and the NFPA, USFA, UL and BRK documents named in Sources, read on 2026-10-04, and confirmed each listing in stock the same day; it exposed no alarm to smoke, timed nothing, prints no health outcome, and reports only figures the cited document states.
- Primary source
- Intertek, Authorization to Mark for Kidde smoke alarms (UL 217:2024 Ed.10) (manufacturer or vendor document)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Best smoke detector: the maker sheets sort them by sensor, battery and interconnect, and NFPA's placement rule matters more than any of it", https://ownerspec.com/air/reviews/best-smoke-detector/, facts verified 4 October 2026.
Every figure above also appears, with its source, in the article. All sources · How OwnerSpec verifies numbers
Sources
- NFPA, Smoke Alarms at Home safety tip sheet (manufacturer or vendor document)
- NFPA, Smoke alarms (manufacturer or vendor document)
- USFA, Smoke alarms (government or regulatory source)
- UL, new smoke alarm standard updates (press release) (standards or certification body)
- UL Code Authority, UL 217 published with new technical requirements (standards or certification body)
- BRK/Resideo, UL 217 8th Edition update notice (manufacturer or vendor document)
- Intertek, Authorization to Mark for Kidde smoke alarms (UL 217:2024 Ed.10) (manufacturer or vendor document)
- Kidde, 20SD10 product page (manufacturer or vendor document)
- Kidde, 20SD10 user guide (manufacturer or vendor document)
- Kidde, 20SA10 product page (manufacturer or vendor document)
- Kidde, i12010S data sheet (manufacturer or vendor document)
- Kidde, i12010S product page (manufacturer or vendor document)
- Kidde, i4618 data sheet (manufacturer or vendor document)
- Kidde, P4010ACS product page (manufacturer or vendor document)
- Kidde, P4010ACS-W product page (manufacturer or vendor document)
- Kidde, interconnecting Kidde alarms with other brands (manufacturer or vendor document)
- First Alert, SM310 dual sensor 10-year smoke alarm (manufacturer or vendor document)
- First Alert, SM210V 10-year smoke alarm with voice (manufacturer or vendor document)
- First Alert, SA511CN2-3ST product page (manufacturer or vendor document)
- First Alert, SC5 Battery smart smoke and CO alarm page (manufacturer or vendor document)
- First Alert store, SC5 and Nest Protect replacement news (manufacturer or vendor document)
- X-Sense, SD2J0AX product page (manufacturer or vendor document)
- Google Home Help, replace your Nest Protect after expiration (manufacturer or vendor document)
- Google, Nest Protect in California and New York (manufacturer or vendor document)
- New York Department of State, residential smoke alarm sales requirements (government or regulatory source)