For multi-story homes
Best Smart Smoke & CO Detectors for Multi-Story Homes (2027)
The best interconnected alarms for 2027: every unit sounds for every event, across floors, wired or wireless.
The short answer
For multi-story homes in 2027, interconnect is non-negotiable: choose X-Sense SC07-W for wireless or First Alert SMICO100 for hardwired.
Our top picks at a glance
- X-Sense SC07-W Wireless InterconnectedInterconnected combo alarms that all sound together, with a 10-year sealed battery.Best wireless interconnect
- Google Nest Protect (2nd Gen)The premium split-spectrum alarm that speaks, self-tests, and lights your path.Best spoken interconnect
- First Alert SMICO100 Hardwired InterconnectedHardwired interconnected combo alarm with battery backup for code-driven replacements.Best hardwired interconnect
- First Alert SCO500B Wireless Interconnected Smoke & CO AlarmA battery combo alarm that wirelessly interconnects up to 16 units, with voice and location alerts.Wireless interconnect with voice location
- First Alert Onelink Safe & SoundA hardwired smoke and CO alarm that doubles as an Alexa smart speaker.Best hardwired upgrade
- Kidde Smart Smoke & CO Detector 30CUAR-WKidde hardwired smart combo alarm with voice alerts and app notifications.Best value combo
- X-Sense SC07The standalone SC07 combo: LCD CO display and 10-year battery, base for interconnected sets.Best LCD combo value
- X-Sense XS0B-MR121 Smart Smoke Detector with Base StationA Wi-Fi smoke alarm kit with voice location alerts and an SBS50 base station.Best budget Wi-Fi smoke
What owners report
Synthesized from recurring themes in long-term owner feedback.
Most praised
- When a basement alarm triggers, hearing the same alert upstairs removes the guesswork about where the problem is
- Voice location announcements across floors tell a family which level to avoid without checking an app first
Common complaints
- Getting every floor re-paired after a router change is the chore multi-story owners dread
- Hardwired replacements on older wiring can turn a simple swap into an electrician visit
The picks, ranked
Every product in this lineup was picked for this use case, ranked with our strongest choices first. If a product from the wider category does not genuinely fit this scenario, it is not listed here.
| # | Product | Award | Sensors | Power | Connectivity | Lifespan | Certification |
|---|---|---|---|---|---|---|---|
| 1 | X-Sense SC07-W Wireless Interconnected | Best wireless interconnect | Photoelectric smoke, electrochemical CO | 10-year sealed lithium battery | RF wireless interconnect (868/915MHz by region) | 10 years | UL 217 and UL 2034, EN standards by region |
| 2 | Google Nest Protect (2nd Gen) | Best spoken interconnect | Split-spectrum smoke, CO, humidity, temperature, occupancy | Battery (6 AA lithium) or hardwired 120V model | Wi-Fi, Thread interconnect between Protects | 10 years, CO sensor rated 10 years | UL 217 and UL 2034 listed |
| 3 | First Alert SMICO100 Hardwired Interconnected | Best hardwired interconnect | Photoelectric smoke, electrochemical CO | 120V hardwired, AA battery backup | Wired interconnect (up to 18 devices) | 10-year alarm life | UL 217 8th edition and UL 2034 listed |
| 4 | First Alert SCO500B Wireless Interconnected Smoke & CO Alarm | Wireless interconnect with voice location | Photoelectric smoke, electrochemical CO | Battery, 2 AA (included) | - | - | - |
| 5 | First Alert Onelink Safe & Sound | Best hardwired upgrade | Photoelectric smoke, electrochemical CO | 120V hardwired with battery backup | Wi-Fi, Bluetooth; Alexa built in | 10-year alarm life | UL 217 and UL 2034 listed |
| 6 | Kidde Smart Smoke & CO Detector 30CUAR-W | Best value combo | Photoelectric smoke, electrochemical CO | Hardwired with 2 AA battery backup (included) | Kidde app enabled, interconnected | - | - |
| 7 | X-Sense SC07 | Best LCD combo value | Photoelectric smoke, electrochemical CO with LCD | 10-year sealed lithium battery | RF interconnect capable; no direct Wi-Fi | 10 years | UL 217 and UL 2034 by regional model |
| 8 | X-Sense XS0B-MR121 Smart Smoke Detector with Base Station | Best budget Wi-Fi smoke | Photoelectric smoke only | Battery powered alarms; base station plug-in | Wi-Fi via SBS50 base station, wireless interconnect | - | - |
Best wireless interconnect
X-Sense SC07-W Wireless Interconnected
Interconnected combo alarms that all sound together, with a 10-year sealed battery.
RF interconnect across a sealed 10-year battery fleet, no electrician required. The multi-story retrofit pick.
Strengths
- Wireless interconnect: one alarm triggers all units
- 10-year sealed lithium battery, zero battery chores
- Photoelectric smoke plus electrochemical CO
- Multi-packs price whole-home coverage reasonably
Limitations
- Remote phone alerts require the optional base station ecosystem
- Brand app ecosystem is younger than Nest or Kidde
- No voice location announcements
| Sensors | Photoelectric smoke, electrochemical CO |
|---|---|
| Power | 10-year sealed lithium battery |
| Connectivity | RF wireless interconnect (868/915MHz by region) |
| Lifespan | 10 years |
| Certification | UL 217 and UL 2034, EN standards by region |
Best for: Multi-story homes needing whole-house sounding without hardwiring.
Skip if: You want phone alerts out of the box; interconnect is RF, app needs the SBS50 base on supported setups.
Best spoken interconnect
Google Nest Protect (2nd Gen)
The premium split-spectrum alarm that speaks, self-tests, and lights your path.
Protects interconnect and announce the room of origin by voice, so a basement event tells upstairs sleepers exactly where the problem is.
Strengths
- Split-spectrum photoelectric sensor reduces cooking false alarms
- Voice alerts name the room and threat before the siren
- Silence from the app when you are nearby
- Nightly Promise self-check and a pathlight that glows on motion
Limitations
- Premium price multiplies across a whole home
- 10-year sealed life means full unit replacement at expiry
- Google Home migration left some legacy Nest app users frustrated
| Sensors | Split-spectrum smoke, CO, humidity, temperature, occupancy |
|---|---|
| Power | Battery (6 AA lithium) or hardwired 120V model |
| Connectivity | Wi-Fi, Thread interconnect between Protects |
| Lifespan | 10 years, CO sensor rated 10 years |
| Certification | UL 217 and UL 2034 listed |
Best for: Homes wanting the best app alerts, voice alarms, and nuisance-alarm intelligence.
Skip if: Budget matters; Protect costs several times a basic smart alarm per room.
Best hardwired interconnect
First Alert SMICO100 Hardwired Interconnected
Hardwired interconnected combo alarm with battery backup for code-driven replacements.
Wired interconnect up to 18 devices meets code-driven multi-story requirements with battery backup for outages.
Strengths
- Hardwired interconnect sounds every alarm for one event
- Photoelectric smoke plus CO with battery backup
- Adapter plugs ease replacement of common legacy brands
- Meets modern code expectations for interconnected coverage
Limitations
- No direct app or voice-assistant alerts
- Hardwired install may need an electrician
- Smart-home value is indirect, via whole-home audibility
| Sensors | Photoelectric smoke, electrochemical CO |
|---|---|
| Power | 120V hardwired, AA battery backup |
| Connectivity | Wired interconnect (up to 18 devices) |
| Lifespan | 10-year alarm life |
| Certification | UL 217 8th edition and UL 2034 listed |
Best for: Replacing hardwired alarms where interconnect sounding is required by code or insurer.
Skip if: You want phone app alerts; this is an interconnected alarm, smart through whole-home sounding, not Wi-Fi.
Wireless interconnect with voice location
First Alert SCO500B Wireless Interconnected Smoke & CO Alarm
A battery combo alarm that wirelessly interconnects up to 16 units, with voice and location alerts.
The SCO500B builds the multi-story network with no wires at all: up to 16 battery units interconnect by RF, every one sounds for any event, and the voice alarm names the room of origin for sleepers two floors up.
Strengths
- Wireless interconnect: when one alarm sounds, all sound, across up to 16 compatible units
- Voice alarm announces the threat type and its programmed location
- Photoelectric smoke sensor reduces cooking nuisance alarms, with an electrochemical CO sensor
- Battery powered with a side-load battery drawer, so no electrician and easy swaps
Limitations
- No app or phone alerts; the interconnect network is local only
- Runs on replaceable AA batteries rather than a sealed 10-year pack
- 7-year limited warranty is shorter than 10-year class rivals
| Sensors | Photoelectric smoke, electrochemical CO |
|---|---|
| Power | Battery, 2 AA (included) |
| Interconnect | Wireless RF, up to 16 compatible units |
| Alarm | 85 dB with voice and location |
| Dimensions | 5.13 x 5.13 x 2.8 in |
| Model | SCO500B |
Sources: First Alert product data, CamelCamelCamel, Amazon listing data
Best for: Renters and multi-story homes wanting whole-home sounding without hardwiring.
Skip if: You want phone app alerts; this network is alarm-to-alarm RF, not cloud-connected.
Best hardwired upgrade
First Alert Onelink Safe & Sound
A hardwired smoke and CO alarm that doubles as an Alexa smart speaker.
Safe and Sound interconnects over the hardwired line with other Onelink and many BRK alarms, so a basement event sounds in the top-floor bedrooms instantly.
Strengths
- Built-in Alexa speaker for music and voice in alarm locations
- Photoelectric smoke plus electrochemical CO sensing
- Hardwired interconnect with other Onelink and many BRK alarms
- Adaptive nightlight and strong First Alert app alerts
Limitations
- Hardwired only; no battery-only version
- Discontinued-line risk: verify current stock and support before whole-home buys
- Speaker features raise the price well above alarm-only rivals
| Sensors | Photoelectric smoke, electrochemical CO |
|---|---|
| Power | 120V hardwired with battery backup |
| Connectivity | Wi-Fi, Bluetooth; Alexa built in |
| Lifespan | 10-year alarm life |
| Certification | UL 217 and UL 2034 listed |
Best for: Hardwired homes wanting Alexa in the ceiling plus premium alarm features.
Skip if: You lack hardwired alarm boxes; Safe and Sound is AC-powered only.
Best value combo
Kidde Smart Smoke & CO Detector 30CUAR-W
Kidde hardwired smart combo alarm with voice alerts and app notifications.
The 30CUAR-W interconnects with other compatible Kidde alarms, giving multi-story homes whole-house sounding plus voice alerts and app notifications at a mid price.
Strengths
- Photoelectric smoke plus electrochemical CO sensing in one unit
- Voice alerts announce the threat in the home
- Kidde app enabled for remote status and notifications
- Interconnects with other compatible Kidde alarms
Limitations
- Hardwired install; not a battery-only retrofit
- Backup batteries are replaceable AA cells, not a sealed 10-year pack
- App features depend on a Kidde account and home Wi-Fi
| Sensors | Photoelectric smoke, electrochemical CO |
|---|---|
| Power | Hardwired with 2 AA battery backup (included) |
| Connectivity | Kidde app enabled, interconnected |
| Dimensions | 5 x 5 x 2 in, 1.3 lb |
| Model | 30CUAR-W |
Best for: Families wanting Kidde alarm credibility plus app alerts in hardwired locations.
Skip if: You have no alarm wiring boxes; this model is hardwired with battery backup.
Best LCD combo value
X-Sense SC07
The standalone SC07 combo: LCD CO display and 10-year battery, base for interconnected sets.
The SC07 can wirelessly link with SC07-W units in mixed X-Sense sets, so a standalone budget combo today becomes part of the whole-house network as you add units floor by floor.
Strengths
- LCD shows real-time CO concentration in PPM
- 10-year sealed battery and sensor life
- Can wirelessly link with SC07-W units in mixed sets
- Lower price than the pure interconnect model
Limitations
- Standalone unit has no direct phone app alerts
- No voice announcements
- App ecosystem requires stepping up to base-station models
| Sensors | Photoelectric smoke, electrochemical CO with LCD |
|---|---|
| Power | 10-year sealed lithium battery |
| Connectivity | RF interconnect capable; no direct Wi-Fi |
| Lifespan | 10 years |
| Certification | UL 217 and UL 2034 by regional model |
Best for: Budget combo coverage and the starting unit for an X-Sense interconnected system.
Skip if: You want phone alerts from this unit alone; smart alerts need interconnected base or Wi-Fi siblings.
Best budget Wi-Fi smoke
X-Sense XS0B-MR121 Smart Smoke Detector with Base Station
A Wi-Fi smoke alarm kit with voice location alerts and an SBS50 base station.
The XS0B set interconnects wirelessly so every unit in the kit sounds together across floors; it covers smoke only, so multi-story homes still need CO sensing on each level.
Strengths
- Wi-Fi phone alerts through the included SBS50 base station
- Voice alerts name the location across 17 preset locations
- Wireless interconnect: when one alarms, the set sounds together
- Test and silence from the X-Sense app
Limitations
- Smoke only; no CO sensor
- Phone alerts route through the base station, not direct Wi-Fi
- Base station needs its own outlet and 2.4GHz Wi-Fi
| Sensors | Photoelectric smoke only |
|---|---|
| Power | Battery powered alarms; base station plug-in |
| Connectivity | Wi-Fi via SBS50 base station, wireless interconnect |
| Alerts | Voice location alerts, app notifications |
| Model | XS0B-MR (kit XS0B-MR121) |
Best for: Apartments and homes needing phone smoke alerts cheaply; smoke only, pair with a CO alarm.
Skip if: You need CO sensing in the same unit; the XS0B-MR is smoke only.
Questions, answered
Why does interconnect matter so much?
A closed bedroom door can muffle a hallway alarm below waking levels. Interconnect puts a full-volume alarm in every area for any single detection.
Can I mix brands in an interconnected set?
Wired BRK-compatible sets often mix; wireless RF sets generally cannot across brands. Keep wireless fleets single-brand and test the full chain after install.
How do I test interconnect?
Use the test button on one unit and confirm every unit sounds, on install and monthly. Interconnect that was never tested is an assumption, not a system.
Battery or hardwired for a retrofit?
Battery interconnected sets like X-Sense avoid wiring entirely and meet many retrofit needs; new construction and code-driven replacements usually specify hardwired with backup.