Smoke, carbon monoxide and gas detectors: which you need and where to put them (2026)

A detector costing less than a takeout dinner is probably the cheapest thing that can save your life. Fires and carbon monoxide poisonings happen most often at night, while you’re asleep and can’t sense anything. The alarm wakes you in time.

The catch is that “detector” means three different devices for three different dangers. Let’s take them one at a time.

Three dangers, three detectors

	Smoke alarm	Carbon monoxide (CO) alarm	Gas detector
Detects	Smoke from a fire	Gas produced by incomplete burning	Leaking unburned gas (natural gas or propane)
Why it’s dangerous	Smoke kills before flames do	No smell, color or taste	Explosion, fire
Standard	UL 217 (US), EN 14604 (Europe/UK)	UL 2034 (US), EN 50291 (Europe/UK)	UL 1484 (US), EN 50194 (Europe/UK)
Where	Ceiling, hallways and bedrooms	Near sleeping areas, rooms with fuel-burning appliances	Natural gas: high, near ceiling. Propane: low, near floor
Lifespan	About 10 years	7–10 years	Per manufacturer, often 5 years or more

Smoke alarms

• Photoelectric (optical): responds well to smoldering fires, the kind started by a cigarette or an electrical fault. The most common type in Europe and widely recommended in the US.
• Heat alarm: for kitchens and garages, where cooking smoke or exhaust would cause false alarms.
• Where: on the ceiling, at least 1 ft (30 cm) from walls and light fittings, in the hallway outside sleeping areas and ideally in every bedroom. In a multi-story home, at least one on every level, including the top of the stairs.
• Where not: in the kitchen (use a heat alarm), in bathrooms, near vents or ceiling fans.

Carbon monoxide alarms

CO is produced when a furnace, boiler, stove, fireplace, water heater or gas range burns incompletely or when flue gases don’t vent. For symptoms and what to do when the alarm sounds, see our guide to carbon monoxide poisoning.

• Where: one near sleeping areas, where you’ll hear it at night, and one in each room with a fuel-burning appliance.
• Distance and height: follow the manufacturer’s instructions. Typically 3–10 ft (1–3 m) from the appliance, not directly above it.
• With a display: shows the CO level, useful to spot a stove starting to vent poorly before the alarm sounds.

Gas detectors

• Natural gas (methane): lighter than air, it collects high up. Mount the detector about 1 ft (30 cm) below the ceiling.
• Propane (LPG): heavier than air, it collects low. Mount the detector about 1 ft (30 cm) above the floor.
• With automatic shutoff valve: some systems close the gas supply when a leak is detected. These are installed by a licensed gas fitter.

If you smell gas, don’t switch lights on or off, don’t use your phone in the room, open windows, shut off the gas if you can, get out and call the emergency number or your gas utility’s emergency line from outside.

What else matters when buying

• Certification (UL or EN, as above) printed on the unit and box. Without it, don’t buy it.
• Sealed 10-year battery: no batteries to change, and the alarm can’t be left without one.
• Interconnection: in a big home, when one sounds, they all sound.
• Hush button: silences false alarms without removing the battery.

Maintenance

• Monthly: press the test button.
• Twice a year: vacuum the dust off.
• When prompted: change the battery (on models without a sealed battery).
• By the date on the unit: replace the alarm.

Add them to your winter preparedness checklist before you fire up the heating. And if you have older parents who heat with a wood stove, a CO alarm makes a very good gift.