# Best carbon monoxide detector: the maker data sheets sort them by power, display, interconnect and end-of-life year, and none of them alarms sooner than the others > Maker sheets compared: Kidde KN-COPP-3 plug-in, 30-999 ppm display, 10-year life; Kidde COB10 sealed 10-year battery; First Alert CO605, 7 years; same UL 2034 bands. | | | |---|---| | Source | https://ownerspec.com/air/reviews/best-carbon-monoxide-detector/ | | Publisher | OwnerSpec (https://ownerspec.com/) | | Published | 2026-10-03 | | Updated | 2026-10-03 | | Facts verified | 2026-10-03 | | Disclosure | Contains affiliate links. OwnerSpec may earn a commission at no cost to the reader. | --- ## Short answer For a house with a gas furnace, a gas water heater or an attached garage and an outlet in the bedroom hallway, the pick is the Kidde KN-COPP-3: its data sheet prints a UL 2034 listing, a 9V battery backup, a display reading 30 to 999 ppm, a Peak Level button, a replace-alarm alert at 10 years and a 10-year limited warranty. Where there is no outlet, the Kidde COB10 prints a sealed 10-year battery, the same UL 2034 line and a 10-year warranty with the battery included. The runner-up plug-in is the First Alert CO605: UL 2034 printed, but a 7-year replacement interval and warranty. No unit here alarms sooner than another: every maker sheet prints the same UL 2034 bands, 70 ppm in 60 to 240 minutes, 150 ppm in 10 to 50 minutes and 400 ppm in 4 to 15 minutes. Skip the smart First Alert SC5 unless you want Wi-Fi and interconnect: its pages print UL 217 but not UL 2034. ## Fact sheet - **Answer:** With a hallway outlet, the pick is the Kidde KN-COPP-3: its data sheet prints UL 2034, a 9V backup, a 30 to 999 ppm display with Peak Level button, and a 10-year end-of-life alert and warranty. Without an outlet, the Kidde COB10 prints a sealed 10-year battery. Every sheet prints the same UL 2034 bands: 70 ppm in 60 to 240 minutes, 150 ppm in 10 to 50, 400 ppm in 4 to 15. - **Comparison basis:** Manufacturer data sheets, manuals and product pages for the Kidde KN-COPP-3, COP, COB, COB10, COBD10, C3010, 30CUD10 and 30CUDR, First Alert's CO605, CO606, CO710, SMCO210 and SC5 pages, X-Sense's SC07 page and ETL manual, and Google's Nest Protect support pages, compared on power source, display and peak memory, interconnect, printed standard, end-of-life interval and warranty; placement from NFPA's and CPSC's public CO pages. - **Assumptions:** The reader lives in the US and the home has at least one fuel-burning appliance, a fireplace or an attached garage; some state codes tie the requirement to those features and others do not; A plug-in alarm sits in an outlet the maker's manual allows; a sealed-battery alarm is replaced, not re-batteried, when it signals end of life; The standard printed on the maker's page is taken as printed; this page did not look up UL's certification directory - **Method:** OwnerSpec compared manufacturer-published specifications read on 2026-10-03 and confirmed each listing in stock the same day; it did not expose any alarm to carbon monoxide, measured no alarm time, prints no health outcome, and reports only the figures the cited document states. - **Primary source:** [Kidde, KN-COPP-3 data sheet](https://www.shareddocs.com/hvac/docs/2001/Public/01/Data_Sheet_Kidde_KN-COPP-3_ENG.pdf) (manufacturer or vendor document) - **Facts verified:** 2026-10-03 - **Last updated:** 2026-10-03 - **Canonical URL (cite this):** https://ownerspec.com/air/reviews/best-carbon-monoxide-detector/ If every appliance in the house is electric and there is no fireplace or attached garage, some state codes do not require a CO alarm at all (Iowa Code 2019 section 100.18 is one): check yours first, because the rest of this page assumes you need one. ## How was this shortlist built? Every figure here is a manufacturer-published specification read on 2026-10-03 from the document named beside it; nothing was exposed to carbon monoxide or timed by this site, and every listing was confirmed in stock the same day. Units were compared on power source, display and peak memory, interconnect, standard printed, end-of-life interval and warranty. A standard number appears only where the maker prints it. UL 2034 is the standard CPSC names for single and multiple station carbon monoxide alarms; CPSC's fact sheet says to install an alarm that meets its current edition. Three named candidates are absent on purpose. First Alert's pages for the CO710 and SMCO210 say the products are no longer available for sale, and no Google Nest Protect was picked: Google's support page sets its 10-year expiry and names the First Alert smart alarm as its replacement. ## How do the CO-only alarms compare on paper? | Model | Power | Display | Interconnect | Standard printed | End of life | Warranty | |---|---|---|---|---|---|---| | Kidde KN-COPP-3 | Plug-in, 9V backup | 30 to 999 ppm, Peak Level button | No | Listed to UL 2034 | Alert at 10 years | 10 years | | Kidde COP | Plug-in, 2 AA backup | None | N/A | UL 2034, NFPA 72, NFPA 101 | 10 years after powered | 10 years, batteries excluded | | First Alert CO605 | Plug-in, 9V backup | None | Not printed | Conforms to UL 2034 | Replace 7 years after installation | 7 years | | Kidde COB10 | Sealed 10-year battery | None, alarm memory LED | N/A | UL 2034, NFPA 72, NFPA 101 | 10 years after powered | 10 years, battery included | | Kidde COBD10 | Sealed 10-year battery | Backlit digital display | N/A | UL 2034 | 10 years after powered | 10 years | | Kidde COB | 2 AA batteries | None | N/A | UL 2034 | 10 years | 10 years, batteries excluded | ## How do the combination smoke and CO alarms compare on paper? | Model | Power | Smoke sensor | Interconnect | Standard printed | End of life | Warranty | |---|---|---|---|---|---|---| | Kidde 30CUD10 | Sealed 10-year battery | Photoelectric | N/A | UL 217 and UL 2034 | 10 years after powered | 10 years, battery included | | Kidde 30CUDR | 2 AA batteries | Photoelectric | N/A | UL 217 and UL 2034 | 10 years | 10 years, batteries excluded | | X-Sense SC07 | Sealed 10-year lithium battery | Photoelectric | Standalone (SC07-W is the wireless sibling) | Page: ETL certified, UL 217; manual: UL 217 and UL 2034 | About 10 years | Not found | | First Alert SC5 Battery | 6 replaceable CR123A | Not printed | Wireless, plus Wi-Fi | UL 217 10th Edition | Not read | 10 years | | First Alert SC5 Hardwire | Hardwired, 3V lithium backup | Not printed | Hardwired, plus Wi-Fi | UL 217 10th Edition | Not read | 10 years | ## Where do CO alarms go, and how many? NFPA's public CO page says to install CO alarms in a central location outside each sleeping area and on every level of the home, plus wherever local law requires, to interconnect them so that when one sounds they all sound, and to follow the maker's instructions for placement and mounting height. CPSC words it differently: each level and outside sleeping areas, but not in attics or basements unless they include a sleeping area. Where the two differ, the maker manual decides. Kidde's C3010 user guide puts a single alarm near the bedrooms, not in the basement or furnace room, because CO may not reach an alarm on another level. Every Kidde CO alarm here prints interconnect N/A or No; the First Alert SC5 is the only unit whose maker prints wireless or hardwired interconnect. A gas water heater that keeps [dropping its pilot](/plumbing/guides/water-heater-pilot-light-wont-stay-lit-thermocouple/) is one reason a basement alarm earns its place. ## Kidde KN-COPP-3: buy it or skip it? Buy it if you want to see a number. Kidde's data sheet prints a display from 30 to 999 ppm updated every 15 seconds and a Peak Level button that recalls the highest reading since the last reset, down to 11 ppm, plus the UL 2034 listing, a 9V backup, 85 dB and a 10-year limited warranty. The flaw is that the display does not make it more sensitive: Kidde's C3010 sheet says its sensor will not alarm below 30 ppm, and the UL 2034 bands match the cheapest unit here. The sheet prints interconnect as No. Skip it if no outlet sits in the hallway outside the bedrooms: the Kidde COBD10 below gives a readout without one. ## First Alert CO605 and Kidde COP: buy them or skip them? Buy the First Alert CO605 if the lowest outlay matters. The First Alert store page prints conforms to UL 2034, 85 dB and an end-of-life timer, and the manual says to replace the alarm 7 years after installation; the warranty is 7 years from purchase. The flaw is the 7 years against Kidde's 10. First Alert's own site now lists the same UPC as model CO606, so the Amazon title and the maker's current name differ. Buy the Kidde COP if you would rather keep AA cells than a 9V: Kidde's sheet prints 2 AA backups, a 10-year end-of-life, a 10-year warranty with batteries excluded, and no display. Skip both if the only outlet is behind furniture or beside a window or door: Kidde's placement page says to avoid dead air spaces and spots next to windows and doors. ## Kidde COB10, COBD10 and COB: buy them or skip them? Buy the Kidde COB10 for a hallway with no outlet. Kidde's data sheet prints a 10-year sealed battery, an end-of-life notice 10 years after it is powered, 85 dB at 10 ft and a 10-year warranty that includes the battery. Buy the Kidde COBD10 for the readout on a sealed battery: its sheet prints the same lines plus a backlit display. The flaw: peak level memory is not printed on the COBD10 sheet, so this page does not claim it. Buy the Kidde COB for a second level where the cheapest UL 2034 unit will do: 2 AA batteries, 10-year end-of-life, 10-year warranty with the batteries excluded. CPSC recommends replacing alarm batteries annually, so the saving over the COB10 goes back into AA cells. Skip all three if you want them to talk to each other: every sheet prints interconnect N/A or No. ## Kidde 30CUD10 and X-Sense SC07: buy them or skip them? Buy the Kidde 30CUD10 if one ceiling unit must cover smoke and CO with both standards in print. Kidde's data sheet prints a photoelectric smoke sensor, UL 217 and UL 2034, a 10-year sealed battery and a 10-year warranty with the battery included. The 30CUDR is the same alarm on 2 AA cells. Buy the X-Sense SC07 for a display on a combination alarm for less. X-Sense's page prints ETL certified, meets UL 217, a 10-year sealed lithium battery, a product life of about 10 years and the same three CO alarm bands. The flaw is the paperwork: UL 2034 appears in the SC07's ETL user manual but not on the product page, and no warranty length was found on X-Sense's site. The SC07 is standalone; the SC07-W is the wireless-interconnect sibling, a different product. Skip both if the house has alarm wiring: a battery unit cannot join a hardwired interconnect. ## First Alert SC5 and Google Nest Protect: buy them or skip them? Buy the First Alert SC5 Battery if you want a phone alert and alarms that sound together. First Alert's page prints wireless interconnect, Wi-Fi, voice alerts, six replaceable CR123A batteries, UL 217 10th Edition and a 10-year limited warranty; First Alert and Google both name it as the Nest Protect replacement. Buy the First Alert SC5 Hardwire where alarm wiring exists: its page prints hardwired interconnect, a 3V lithium backup and the same UL 217 and warranty lines. The flaw is the standard line: neither SC5 page prints UL 2034, only UL 217. Google's support page says the 2nd gen Nest Protect must be replaced after 10 years from its date of manufacture, and that the First Alert alarm can relay a smoke or CO event to it. Skip the SC5 if you only need CO cover in a hallway: a Kidde COB10 does that without Wi-Fi. **Count outlets and levels before you buy** Do not order until you have two numbers: how many levels the house has, and how many spots outside each sleeping area have an outlet. Each outlet position takes a KN-COPP-3 or CO605, each bare position a COB10, and a house with alarm wiring takes the SC5 Hardwire. Write the install date on every unit: the end-of-life beep arrives in year 7 or 10. ## Who should skip a CO alarm? Fewer people than the exemptions suggest. Iowa Code 2019 section 100.18, as printed, requires CO alarms in dwellings with a fuel-fired heater or appliance, a fireplace or an attached garage, so an all-electric Iowa home without a garage falls outside it. Other states and towns word their rules differently, and NFPA's page adds "other locations where required by applicable laws, codes or standards". Check the local rule before deciding you are exempt. EPA's indoor air page lists the home sources: unvented kerosene and gas space heaters, leaking chimneys and furnaces, back-drafting appliances, gas stoves, generators and exhaust from attached garages. With none of those, the code question is the only one left. ## What goes wrong? **The alarm beeps and gets its battery changed.** Kidde's FAQ says a quick beep every 30 seconds with a flashing red LED means end of life after 7 or 10 years, and a new battery will not stop it. The [CO alarm beeping guide](/air/guides/carbon-monoxide-detector-beeping-what-it-means/) sorts that signal from a low battery and a real alarm. **The smoke side chirps and gets blamed on CO.** The [smoke detector chirping guide](/air/guides/smoke-detector-chirping-low-battery-end-of-life/) covers the low-battery and end-of-life patterns on a combination unit. **A natural gas leak is expected to set it off.** Kidde's user guide says CO alarms cannot detect natural gas, propane or other combustible fuels. ## The picks - **Kidde KN-COPP-3 (plug-in, 9V backup, digital display)**: Has a hallway outlet and wants to read the ppm number (Kidde data sheet: 120 VAC plug-in with 9V battery backup, digital display 30 to 999 ppm updated every 15 seconds, Peak Level button, 85 dB, listed to UL 2034, replace-alarm alert at 10 years, 10-year limited warranty) Amazon: https://www.amazon.com/dp/B00002N86A/?tag=ownerspec-20 - **Kidde COP (plug-in, 2 AA backup)**: Wants a plug-in with AA backup batteries instead of a 9V (Kidde data sheet: 120 VAC with 2 AA backup batteries, no display, interconnect N/A, end-of-life notification 10 years after powered, 10-year limited warranty with batteries excluded, meets UL 2034, NFPA 72 and NFPA 101 at date of manufacture) Amazon: https://www.amazon.com/dp/B0G1CPTKNQ/?tag=ownerspec-20 - **First Alert CO605 (plug-in, 9V backup)**: Wants the cheapest plug-in and accepts a 7-year replacement (First Alert store page: conforms to UL 2034, 85 dB, end-of-life timer, 7-year limited warranty; manual: replace alarm 7 years after installation; First Alert now lists the same UPC as model CO606) Amazon: https://www.amazon.com/dp/B000ND74XA/?tag=ownerspec-20 - **Kidde COB10 (sealed 10-year battery)**: No outlet near the bedrooms and never wants to change a battery (Kidde data sheet: 10-year sealed battery, no display, alarm memory LED, 85 dB at 10 ft, interconnect N/A, end-of-life notice 10 years after powered, 10-year limited warranty with the battery included, meets UL 2034, NFPA 72 and NFPA 101 at date of manufacture) Amazon: https://www.amazon.com/dp/B0G1CDKYSJ/?tag=ownerspec-20 - **Kidde COBD10 (sealed 10-year battery, backlit display)**: Wants the sealed battery and a readout, without an outlet (Kidde data sheet: same as the COB10 plus a backlit digital display; interconnect N/A; UL 2034 at date of manufacture; 10-year limited warranty; peak level memory is not printed on this sheet) Amazon: https://www.amazon.com/dp/B0G1CDKYSD/?tag=ownerspec-20 - **Kidde COB (2 AA batteries)**: Wants the lowest-cost battery alarm for a second level (Kidde data sheet: 2 AA batteries, no display, interconnect N/A, 10-year end-of-life notification, 10-year limited warranty with batteries excluded, UL 2034 at date of manufacture) Amazon: https://www.amazon.com/dp/B0G1CR88J9/?tag=ownerspec-20 - **Kidde 30CUD10 (smoke + CO, sealed 10-year battery)**: Wants one unit for smoke and CO with both standards printed (Kidde data sheet: photoelectric smoke sensor plus CO sensor, 10-year sealed battery, interconnect N/A, end-of-life alert at 10 years, 10-year limited warranty with battery included, meets UL 217 and UL 2034 (plus NFPA 72 and NFPA 101) at date of manufacture) Amazon: https://www.amazon.com/dp/B0CX6BWRMM/?tag=ownerspec-20 - **X-Sense SC07 (smoke + CO, sealed 10-year battery, 1-pack)**: Wants a combination alarm with a display at a lower outlay (X-Sense product page: ETL certified, meets UL 217, photoelectric smoke plus electrochemical CO, 10-year sealed lithium battery, product life about 10 years, 85 dB at 3 m; the ETL user manual prints UL 217 and UL 2034; standalone, the SC07-W is the wireless sibling; no warranty length found) Amazon: https://www.amazon.com/dp/B09P52JX2R/?tag=ownerspec-20 - **First Alert SC5 Battery smart smoke + CO alarm (SMCO600NV)**: Wants Wi-Fi alerts and wireless interconnect, or replaces a Nest Protect (First Alert page: wireless interconnect, Wi-Fi, voice alerts, 6 replaceable CR123A batteries, conforms to UL 217 10th Edition, 10-year limited warranty, named by First Alert and Google as the Nest Protect replacement; UL 2034 is not printed on the page) Amazon: https://www.amazon.com/dp/B0DS2W3794/?tag=ownerspec-20 - **First Alert SC5 Hardwire smart smoke + CO alarm (SMCO600NV-AC)**: Has existing hardwired alarm wiring and wants the smart features (First Alert page: hardwired interconnect, 3V lithium backup, Wi-Fi, voice alerts, conforms to UL 217 10th Edition, 10-year limited warranty; UL 2034 is not printed on the page) Amazon: https://www.amazon.com/dp/B0DS2VG4P1/?tag=ownerspec-20 ## Frequently asked questions ### How many carbon monoxide alarms does a house need, and where do they go? NFPA's public CO page says to install CO alarms in a central location outside each sleeping area and on every level of the home, interconnected where possible, and to follow the maker's instructions for placement and mounting height. CPSC words it as each level and outside sleeping areas, but not in attics or basements unless they include a sleeping area. The maker manual settles the mounting. ### Does a more expensive carbon monoxide detector alarm at a lower level? Not on paper. Kidde's C3010 and COB10 data sheets and X-Sense's SC07 page print the same UL 2034 alarm bands: 70 ppm in 60 to 240 minutes, 150 ppm in 10 to 50 minutes and 400 ppm in 4 to 15 minutes, and Kidde says the sensor will not alarm below 30 ppm. Extra money buys a display, a sealed battery or a longer warranty, not a lower threshold. ### Do carbon monoxide alarms expire? Yes. Kidde's replacement FAQ says a quick beep every 30 seconds with a flashing red LED means the unit has reached the end of its 7 or 10-year lifespan, and that replacing the batteries will not stop it. Kidde prints 10 years on every alarm here, and First Alert's CO605 manual says to replace the alarm 7 years after installation. ### Is a combination smoke and CO alarm as good as two separate alarms? Check both standard numbers are printed. Kidde's 30CUD10 and 30CUDR data sheets print UL 217 for smoke and UL 2034 for CO; First Alert's SC5 pages print UL 217 10th Edition only. The counts also differ: NFPA's smoke alarm page puts a smoke alarm in every sleeping room, while its CO page puts a CO alarm outside each sleeping area and on every level. ### Should 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 names the First Alert Smart Smoke & Carbon Monoxide Alarm as a compatible replacement when used with the Google Home app. The two can relay a smoke or CO event to each other. This page picks the First Alert SC5 for that role and lists no Nest Protect. ## Sources - [NFPA, Carbon Monoxide safety](https://www.nfpa.org/education-and-research/home-fire-safety/carbon-monoxide) (manufacturer or vendor document) - [NFPA, Smoke alarms](https://www.nfpa.org/education-and-research/home-fire-safety/smoke-alarms) (manufacturer or vendor document) - [CPSC, CO Alarms](https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/Carbon-Monoxide-Information-Center/CO-Alarms) (government or regulatory source) - [CPSC, Carbon Monoxide Fact Sheet](https://www.cpsc.gov/safety-education/safety-guides/carbon-monoxide/carbon-monoxide-fact-sheet) (government or regulatory source) - [CPSC, Carbon Monoxide Alarms (voluntary standards)](https://www.cpsc.gov/Regulations-Laws--Standards/Voluntary-Standards/Carbon-Monoxide-Alarms) (government or regulatory source) - [EPA, Carbon Monoxide's Impact on Indoor Air Quality](https://www.epa.gov/indoor-air-quality-iaq/carbon-monoxides-impact-indoor-air-quality) (government or regulatory source) - [Iowa Code 2019, section 100.18](https://www.legis.iowa.gov/docs/code/2019/100.18.pdf) (government or regulatory source) - [Kidde, KN-COPP-3 data sheet](https://www.shareddocs.com/hvac/docs/2001/Public/01/Data_Sheet_Kidde_KN-COPP-3_ENG.pdf) (manufacturer or vendor document) - [Kidde, COP product data sheet](https://brand.kidde.com/m/e0001a6a57c82f9/original/PDS_COP.pdf) (manufacturer or vendor document) - [Kidde, COB10 product data sheet](https://brand.kidde.com/m/20ffb7a8ddc1715d/original/PDS_COB10.pdf) (manufacturer or vendor document) - [Kidde, COBD10 product data sheet](https://brand.kidde.com/m/1a78f4f81c929895/original/PDS_COBD10.pdf) (manufacturer or vendor document) - [Kidde, COB product data sheet](https://brand.kidde.com/m/20060f1bcbe640d2/original/PDS_COB.pdf) (manufacturer or vendor document) - [Kidde, plug-in CO alarm user guide](https://brand.kidde.com/m/404472a7b56224b5/original/UG_CO-AC-Plug-In_En.pdf) (manufacturer or vendor document) - [Kidde, 30CUD10 product data sheet](https://brand.kidde.com/m/5c85dd7b2579b28e/original/PDS_30CUD10.pdf) (manufacturer or vendor document) - [Kidde, 30CUDR product data sheet](https://brand.kidde.com/m/39447bd3cdbd6d65/original/PDS_30CUDR.pdf) (manufacturer or vendor document) - [Kidde, C3010 data sheet](https://www.shareddocs.com/hvac/docs/2001/Public/03/Data_Sheet_Kidde_C3010_ENG.pdf) (manufacturer or vendor document) - [Kidde, C3010 and C3010-D user guide](https://www.shareddocs.com/hvac/docs/2001/Public/0C/User-Guide-C3010-C3010-D-Eng.pdf) (manufacturer or vendor document) - [Kidde, CO alarm replacement FAQs](https://www.kidde.com/support/carbon-monoxide-alarms/replacement-faqs) (manufacturer or vendor document) - [First Alert store, CO605 product page](https://www.firstalertstore.com/store/products/co605-plug-in-carbon-monoxide-alarm-with-battery-backup.htm) (manufacturer or vendor document) - [First Alert, CO605 user manual](https://www.firstalertstore.com/store/images/pdf/CO605-First_Alert_Plug-In_Carbon_Monoxide_Alarm_with_Battery_Backup.pdf) (manufacturer or vendor document) - [First Alert, CO606 plug-in product page](https://www.firstalert.com/products/carbon-monoxide-plug-in-alarm-with-battery-backup) (manufacturer or vendor document) - [First Alert, CO710 product page](https://www.firstalert.com/products/carbon-monoxide-alarm-with-10-year-battery-and-digital-temperature-display) (manufacturer or vendor document) - [First Alert, SMCO210 product page](https://www.firstalert.com/products/10-year-battery-2-in-1-smoke-carbon-monoxide-alarm-with-slim-profile-design) (manufacturer or vendor document) - [First Alert, SC5 Battery smart smoke and CO alarm page](https://www.firstalert.com/products/sc5-battery-smart-smoke-carbon-monoxide-alarm) (manufacturer or vendor document) - [First Alert, SC5 Hardwire smart smoke and CO alarm page](https://www.firstalert.com/products/sc5-hardwire-smart-smoke-carbon-monoxide-alarm) (manufacturer or vendor document) - [X-Sense, SC07 product page](https://www.x-sense.com/products/10-year-battery-combination-smoke-carbon-monoxide-alarm-with-lcd-sc07) (manufacturer or vendor document) - [X-Sense, SC07 ETL user manual](https://download.x-sense.com/instructions/sc07-user-manual-etl.pdf) (manufacturer or vendor document) - [Google Home Help, replace your Nest Protect after expiration](https://support.google.com/googlehome/answer/15731767?hl=en) (manufacturer or vendor document) - [Google Home Help, set up your First Alert Smart Smoke & CO Alarm](https://support.google.com/googlehome/answer/16324143?hl=en) (manufacturer or vendor document) --- Citation: OwnerSpec, "Best carbon monoxide detector: the maker data sheets sort them by power, display, interconnect and end-of-life year, and none of them alarms sooner than the others", https://ownerspec.com/air/reviews/best-carbon-monoxide-detector/, facts verified 3 October 2026. 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