How to Choose Smoke & CO Detectors

A smoke or carbon monoxide alarm is the cheapest life-saving device you’ll ever buy — and the one most people ignore until the low-battery chirp drives them crazy at 3 a.m. Choosing the right sensor, in the right spot, with a battery you don’t have to think about, is a genuine safety decision, not a shopping errand.

Smoke, CO, or both?

These are two completely different hazards. A smoke alarm detects particles from a fire. A carbon monoxide alarm detects an odorless, colorless gas produced by anything that burns fuel — a furnace, gas range, water heater, fireplace, or a car left running in an attached garage. One will not catch the other, so a safe home needs both kinds of coverage.

You can cover both jobs two ways: buy dedicated smoke alarms plus dedicated CO alarms, or buy combination smoke/CO units that stack both sensors in one housing. Combination units mean fewer devices on the ceiling and one test button, but if one sensor fails you replace the whole unit. Brands like First Alert and Kidde make both styles, and you’ll find them alongside the rest of our home & personal security gear.

Ionization vs. photoelectric — and why you want both

Smoke alarms use one of two sensing technologies, and they are genuinely better at different fires:

Fire-safety experts recommend having both technologies in the home. The simplest way to do that is to buy dual-sensor alarms, which put both sensors in one unit. If you buy single-sensor alarms instead, mix them — photoelectric near living rooms and bedrooms (where smoldering fires start), ionization near stairwells.

Tip: Photoelectric alarms trip less around kitchen steam and cooking, so they’re the better choice for the hallway just outside a kitchen. Never disable an alarm because it’s “too sensitive” — move it or swap the sensor type instead.

Batteries: sealed 10-year vs. replaceable

This one decision saves the most headaches. A sealed 10-year lithium alarm never needs a battery change — you install it, and it self-retires in a decade when the sensor is worn out anyway. No chirping, no ladder trips, no dead battery on the one night it matters.

Hardwired alarms wire into house power and interconnect so they all sound at once — required by code in most new construction. They still carry a backup battery for outages; if yours uses a replaceable backup, keep a few 9V and lithium coin cells in your battery drawer. Whatever you choose, test every alarm monthly and replace the whole unit after 10 years (CO units often expire in 7).

Placement, interconnection, and the smart-alarm question

Detectors only work where they can “see” smoke or gas early. The rules are simple:

• Smoke: one in every bedroom, one outside each sleeping area, and at least one per level including the basement.
• CO: one outside each sleeping area and on every level; keep them at least 15 feet from fuel-burning appliances to avoid nuisance trips.
• Mount smoke alarms on the ceiling or high on the wall — smoke rises. CO mixes with air, so most CO units can sit at any height.
• Keep smoke alarms at least 10 feet from the stove and away from bathroom steam.
• You’ll want a stable ladder or step stool for ceiling installs — don’t balance on a chair.

Interconnected alarms all sound together, so an alarm in a far basement wakes someone sleeping upstairs. Hardwired alarms interconnect by wire; many battery models interconnect wirelessly. Smart alarms (Google Nest Protect, First Alert Onelink) add phone alerts, voice location announcements, and app-based hush — worth it for large homes, rentals you monitor remotely, or anyone hard of hearing.

Don’t stop at the alarm

An alarm buys you time; an exit plan and the right gear use it. Keep a rated fire extinguisher on each level near an exit, a flashlight or two where you can grab them in the dark, and a lantern in case a fire or CO leak knocks out power. A few plug-in night lights along hallways make a dark escape route far easier to follow. Round it out with the basics in our safety equipment aisle.

Pick by your home

Frequently asked questions

Smoke and CO alarms are the rare purchase where the cheap, boring choice is also the right one — buy sealed, cover every level, and test monthly. For hands-on advice or to see the alarms in person, visit your local independent hardware store, or ask us here and we’ll point you to the right setup for your home.