We checked real listings and manufacturer specs for five smoke and smoke/CO combo detectors from First Alert, X-Sense and Kidde, comparing sensor type, battery life and connectivity.
First Alert
Why we like it
First Alert
Why we like it
X-Sense
Why we like it
X-Sense
Why we like itKidde
Why we like it| Product | Rank | Brand | Best For | Score |
|---|---|---|---|---|
| First Alert 10-Year Battery Combination S... | #1 | First Alert | Best Overall (Combo Smoke + CO, No Battery Maintenance) | 9.8 |
| First Alert Battery Smoke Alarm | SMI100 | #2 | First Alert | Best Simple, Single-Hazard Alarm | 9.6 |
| X-Sense Wireless Interconnected Smoke Det... | #3 | X-Sense | Best Whole-Home Interconnect Without Wi-Fi | 9.4 |
| X-Sense Smart Smoke Detector Fire Alarm w... | #4 | X-Sense | Best for Remote Phone Alerts | 9.3 |
| Kidde Hardwired Smoke & Carbon Monoxide D... | #5 | Kidde | Best Hardwired Combo with Voice Alerts | 9.1 |
Buyer checklist
This is desk research, not a hands-on smoke or CO exposure test. As with other guides in this series, Amazon's live listing pages for all five detectors returned automated bot-check screens during our research, and the Internet Archive's Wayback Machine was offline for this research window, so we pulled every spec from each manufacturer's own current product page and could not confirm live Amazon star ratings for any of the five units. Two of our five originally-drafted candidates turned out to be discontinued during research, and we're disclosing both substitutions rather than writing up dead listings. First Alert's own store lists the SC7010BV (a hardwired talking smoke/CO combo) as discontinued with no restock date, so we replaced it with the SMCO210, First Alert's current 10-year-battery smoke/CO combo. Separately, First Alert's store lists the SA303CN3 (a basic ionization smoke alarm) as discontinued, with the manufacturer explicitly directing shoppers to the SMI100 as its replacement — we used that manufacturer-recommended successor rather than the dead model. We also swapped our originally-planned Google Nest Protect pick: its official Google Store page consistently redirected to a region/consent-gated page during our research session rather than loading normally, and several third-party retailer pages we tried to check for cross-verification returned access-denied errors. Rather than describe a product we couldn't independently verify through any channel this session, we substituted the X-Sense XS01-WX, a comparably positioned Wi-Fi-connected smart smoke alarm we could fully verify against X-Sense's own site. Sensor technology matters here: ionization sensors (First Alert SMI100, and one of the two sensors in the Kidde combo) tend to respond faster to flaming fires, while photoelectric sensors (X-Sense's alarms, and one sensor in the First Alert combo) tend to respond faster to smoldering fires. Fire-safety authorities generally recommend either dual-sensor alarms or a mix of both types in a home rather than relying on one sensor type exclusively — check each product's own documentation for its specific sensor combination.
Per general fire-safety guidance echoed in these manufacturers' own materials, ionization sensors tend to detect fast, flaming fires slightly faster, while photoelectric sensors tend to detect slow, smoldering fires slightly faster. Some products in this guide (like the First Alert SMCO210 and Kidde i12010SCO) combine sensor types specifically to cover both fire behaviors in one unit.
It depends on what you want. Per X-Sense's own materials, the XS01-WR interconnects multiple alarms via RF so they all sound together, without needing Wi-Fi, an app, or a subscription. The XS01-WX adds Wi-Fi and app notifications so you can be alerted even when you're not home to hear the alarm — a real benefit if you travel or want remote awareness, but with more setup and reliance on your home network staying up.
Per the manufacturers' own stated design, a sealed 10-year lithium battery is built to last the alarm's full rated service life, after which the entire unit (not just the battery) is meant to be replaced — these units include an end-of-life warning specifically because the sealed battery isn't user-replaceable. This differs from alarms using a standard 9V battery, which need periodic battery swaps but can keep running past that with fresh batteries as long as the alarm itself is still within its service life.
We planned to include one, but its official Google Store listing kept redirecting to a region/consent page rather than loading normally during our research session, and other retailer pages we tried for cross-verification returned access-denied errors. Rather than describe specs we couldn't verify through any channel this session, we substituted a comparable Wi-Fi-connected smart alarm (X-Sense XS01-WX) that we could fully verify.