The Best Smoke and CO Detector Combos

This is the standard-issue combo alarm, and there is nothing wrong with standard issue. The photoelectric smoke sensor is the right type for the slow, smoldering fires that start in bedrooms and living rooms, and the electrochemical CO cell is the same technology the expensive units use. It mounts on two screws, takes AA batteries you already own, and the test button is big enough to hit with a broom handle.

The tradeoff is the battery. You will be on a ladder changing it every year, and the 3 a.m. low-battery chirp is a real phenomenon with a documented history of ending up in a junk drawer. Buy it for a single room. Think harder before buying six.

• Power2 AA batteries
• Smoke sensorPhotoelectric
• CO sensorElectrochemical
• InterconnectNone
• ListingsUL 217 / UL 2034

Skip it if: you are buying for the whole house at once. Sealed 10-year units cost a little more per room and erase a decade of battery chirps.

The sealed battery is the whole argument. It lasts the full ten-year service life of the alarm, so the battery dies when the unit is due for replacement anyway. No chirps at 3 a.m., no battery drawer, no ladder in January. The voice alert matters more than it sounds: the unit says whether it found smoke or carbon monoxide, which tells you whether to crawl low or open windows.

Several states now require sealed 10-year units when battery alarms get replaced, so this is also the buy-once-and-comply option for rentals. The deactivation switch kills it permanently at end of life so it cannot be returned to service with a dead sensor.

• PowerSealed 10-year lithium
• Smoke sensorPhotoelectric
• Voice alertAnnounces hazard type
• InterconnectNone
• ListingsUL 217 / UL 2034

Skip it if: your local code requires hardwired alarms in your situation, which is common in new construction and major remodels.

X-Sense is the newer name on this list and the SC07 competes hard on hardware. The LCD screen shows the actual CO concentration in parts per million instead of a bare siren, which is useful for catching low-level CO from a struggling furnace before it ever reaches alarm threshold. The sealed 10-year battery and dual UL listings match the Kidde spec for spec.

I rank it below the Kidde only on track record, not on performance. If the readout appeals to you, mount one near the mechanical room and let it keep an eye on the furnace.

• PowerSealed 10-year lithium
• Smoke sensorPhotoelectric
• DisplayLCD shows CO level
• InterconnectNone
• ListingsUL 217 / UL 2034

Skip it if: you want a brand your local fire department has stocked for decades. First Alert and Kidde have longer track records.

If your ceiling boxes already have the orange three-wire connector, this is the drop-in replacement. Hardwired alarms interconnect over that third wire, so a basement alarm wakes the upstairs bedrooms. That whole-house trigger is the single biggest upgrade in fire safety, and the NFPA placement guidance assumes it in newer homes.

One honest note: the SC9120B uses an ionization smoke sensor, which responds fastest to flaming fires and slower to smoldering ones. It is fine as part of a mixed house. Pair it with photoelectric units like the Kidde or the SCO5CN so both fire types are covered, and keep ionization units a good ten feet from the kitchen or the toaster will own your mornings.

• Power120V AC, battery backup
• Smoke sensorIonization
• InterconnectWired, up to 18 units
• InstallStandard junction box
• ListingsUL 217 / UL 2034

Skip it if: your house has no existing alarm wiring. Running new cable through finished ceilings costs more than a full set of wireless interconnect units.

This is the modern answer to the old wiring problem. Each unit talks to the others by radio, so when the basement alarm trips, the bedroom units sound too. You get the whole-house behavior of a hardwired system with nothing but a drill and twelve screws. Pairing is a button press per unit and took me under ten minutes for the set.

Six units is not overkill. Count your code points: each bedroom, each hallway outside sleeping areas, each level. Most two-story houses consume the whole pack with none left over. This is the pick I would hand a new homeowner.

• PowerSealed 10-year lithium
• Smoke sensorPhotoelectric
• InterconnectWireless RF, all units sound
• CoverageSix rooms per pack
• ListingsUL 217 / UL 2034

Skip it if: you live in a small single-level home where one or two standalone units already cover every code point.

Smart alarms get oversold, so here is the narrow truth: the phone alert only matters when nobody is home to hear the siren. That makes this the right unit for a rental property, a second home, or the house of an aging parent. The alarm pushes a notification the moment it trips, names which room, and the app shows battery health without a ladder.

It connects straight to Wi-Fi with no hub, which is the feature that separates current smart alarms from the flaky first generation. In a house you sleep in every night, spend the difference on more of the interconnected 6-pack instead.

• PowerSealed 10-year lithium
• Smoke sensorPhotoelectric
• AlertsPhone push via Wi-Fi, no hub
• AppBattery and sensor status
• ListingsUL 217 / UL 2034

Skip it if: you are home most nights. A siren you can hear beats an app notification you might miss, and the cheaper picks sound the same siren.