Best Smart Smoke and CO Detector: Phone Alerts, Interconnect, No Fees

NFPA 72 calls for a smoke alarm inside every bedroom, outside each separate sleeping area, and on every level of the home including the basement. A two-story, three-bedroom home with a basement typically needs at least 6: one per bedroom, one in the upstairs hall, one on the main floor and one in the basement. Local code can require more.

Put a CO alarm outside each sleeping area and on every level of the home, and follow any extra locations your local code requires. Combination smoke and CO alarms cover both in one device. Homes with gas appliances, a fireplace or an attached garage have CO sources and need them most.

Replace smoke alarms 10 years after the manufacture date printed on the back, per NFPA. Combination alarms with a sealed 10-year battery, such as the X-Sense XP0H-WN, are replaced as a whole unit at that point. Test every alarm monthly.

It is worth it if your home is ever empty, if you have pets, or if you own a rental or second home, because the alarm reaches your phone wherever you are. A standard alarm only warns people inside the house. The Kidde and First Alert alarms here send alerts with no subscription.

Not for phone alerts on these models. Kidde's Ring-connected alarm sends smoke, CO and low battery alerts for free, and an optional Ring plan adds 24/7 professional monitoring at $5 a month, which is $60 a year. First Alert's SC5 sends alerts through its app.

Google stopped making the Nest Protect in 2025 and pointed buyers to First Alert smart alarms. The First Alert SC5 listing states it is compatible with Nest Protect alarms, so you can replace them one at a time. The SC5 comes in battery and hardwired versions.

Replace hardwired alarms with hardwired alarms; the International Residential Code (R314) requires new homes to have hardwired, interconnected alarms with battery backup. Battery alarms suit older homes without that wiring and need no electrician. Wireless interconnect, as on the Kidde and X-Sense picks, links battery alarms without new wire.

When one alarm detects smoke or CO, every linked alarm in the house sounds too. That way a fire in the basement wakes someone in an upstairs bedroom. NFPA recommends interconnecting alarms, and it is required in new construction.

Yes, battery alarms still detect and sound locally, and hardwired alarms fall back on their backup battery. Phone alerts stop until Wi-Fi returns, unless your router is on a battery backup. A small UPS on the router keeps alerts flowing through short outages.

Photoelectric sensors respond faster to slow, smoldering fires and tend to cause fewer cooking nuisance alarms, while ionization responds faster to flaming fires. Groups such as the NFPA recommend having both types or dual-sensor alarms. The X-Sense XP0H-WN uses a photoelectric smoke sensor.