For protecting a home, choose a fixed natural gas alarm certified to a recognized standard (EN 50194 in Europe, UL 1484 in the US), with a catalytic or semiconductor methane sensor set to alarm at 10 to 20 percent LEL, mains power with battery backup, and mount it high on the wall near the gas appliances because methane rises. For finding a leak, choose a handheld sniffer with a gooseneck probe and sensitivity around 50 ppm. Both belong in a home with gas; only the fixed alarm provides continuous protection.
Fixed alarms
| Feature | Look for |
|---|---|
| Certification | EN 50194-1 (domestic gas alarms) or UL 1484; the mark on the unit |
| Gas | Methane (natural gas) for mains gas; LPG models for propane and butane; some cover both with two sensors |
| Alarm point | 10 to 20% LEL; certified units are set within the standard |
| Sensor life | 5 to 10 years; end-of-life indication |
| Power | Mains with battery backup preferred; battery-only units exist |
| Outputs | Relay or valve output to close an automatic gas shut-off valve; interconnection to other alarms; app notification on smart units |
| Mounting | High for methane (near the ceiling); low for LPG (near the floor) |
| Test and silence | Test button; silence with re-alarm |
Where to mount
- Methane: 15 to 30 cm below the ceiling, 1 to 3 m horizontally from the appliance or meter, not directly above the cooker (steam and grease foul sensors), not near windows, doors or extract fans.
- LPG: 15 to 30 cm above the floor, near the appliance or cylinder, not where it will be kicked or splashed.
- One per room with a gas appliance, plus the meter cupboard or boiler room.
Handheld sniffers
For locating leaks at fittings, valves, appliance connections and cylinders, a semiconductor sniffer with a gooseneck, adjustable sensitivity and a tick-rate indication. See how to choose a combustible gas leak detector. A sniffer is not a substitute for the fixed alarm, since it is not watching when you are asleep.
Combination and smart units
Combined gas and CO alarms save wall space; check each function carries its own certification. Smart alarms add phone alerts and integration with a shut-off valve; the certification of the gas-sensing function is still the thing to verify. See CO meter vs CO alarm for the CO side.
Maintenance
- Test monthly with the button (checks electronics and sounder, not the sensor).
- Keep the sensor grille free of grease and dust; do not spray cleaners near it.
- Replace at the end-of-life date on the unit. See sensor lifespan.
- If it alarms: do not switch anything electrical, open windows and doors, leave, turn off the gas at the meter if safely reachable, and call the gas emergency number.
Units
Alarms are set in %LEL; sniffers indicate in ppm or a relative scale. Methane’s LEL is 5 percent by volume, so a 10 %LEL alarm is 5,000 ppm, while a sniffer finds leaks at tens of ppm at the fitting. See PPM vs %LEL in gas detection and understanding ppm, %LEL and %volume. Detectors are in the gas detection category.
Recommended Tools
Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.
Frequently Asked Questions
Where should a natural gas alarm be mounted?
Methane is lighter than air, so mount it high: within about 30 cm of the ceiling, 1 to 3 m from the appliance, away from vents, windows and cooker steam. LPG (propane, butane) is heavier and needs a low-mounted alarm near the floor.
Is a CO alarm the same as a gas alarm?
No. CO alarms detect carbon monoxide from incomplete combustion; natural gas alarms detect methane from a leak. Homes with gas appliances benefit from both; some combination units include both sensors.
How long does a natural gas alarm last?
Sensors typically last 5 to 10 years; the unit states its replacement date. Test monthly with the button and replace at the date, or earlier if it fails a test.
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