First Alert GCO1CN Combination Gas & CO Alarm Review

Quick answer

The GCO1CN is a plug-in alarm that detects both combustible gas (propane and natural/methane) and carbon monoxide in one unit, with a digital display showing which hazard triggered and, for CO, the peak level recorded. According to First Alert's own engineering spec sheet, it's listed to both UL 1484 (gas) and UL 2034 (CO) -- a named, specific standard claim, not just a generic "listed" badge. It's a reasonable single-device option for someone who wants both hazards covered without two separate alarms, with the caveat that it needs to be plugged in at a specific height depending on which gas matters most in your home.

What it does

Per First Alert's architectural and engineering specification for this alarm, it combines an electrochemical CO sensor with a metal-oxide combustible-gas sensor in one 120V AC plug-in unit with a 9V alkaline battery backup. A backlit digital display shows "GAS" or a CO reading depending on what's detected, and a "peak level" button recalls the highest CO level the unit has seen. The spec sheet notes a mounting detail worth calling out because it's easy to miss: methane is lighter than air and rises, so the unit should be mounted high for methane detection; propane is heavier than air and sinks, so it should be mounted low for propane. CO itself, per the same document, disperses evenly through a house, so CO detection isn't height-sensitive.

Key specifications

According to First Alert's spec sheet for this model family:

• Sensors: Electrochemical (CO) + metal oxide (combustible gas -- propane and natural/methane)
• Certification: Listed to UL 1484 and UL 2034 standards (named explicitly on the spec sheet)
• Audible alarm: Piezo horn, manufacturer-rated at 85 dB at 10 feet
• Power: 120V AC plug-in with 9V alkaline battery backup
• Operating temperature range: 40-100°F (4-38°C)
• Operating humidity range: 10-95% relative humidity
• Silence features: Low-battery chirp can be silenced for up to 8 hours; a nuisance alarm can be silenced for several minutes
• Warranty: 5-year limited

What we like

• Two real hazards, one device, one named standard for each. The UL 1484 (gas) and UL 2034 (CO) claims are both specific and both stated on the same document, not scattered or implied.
• The mounting-height guidance is genuinely useful and specific. Methane-high, propane-low, CO-anywhere is the kind of detail a generic "mount on the wall" instruction would miss, and it's stated plainly rather than buried.
• Peak-level memory for CO. Useful for the same reason the Kidde C3010's Event Memory is useful: it can tell you something happened even after the immediate alarm condition clears.

Limitations

• AC-outlet dependent. This is a plug-in unit with only a 9V backup battery for power outages -- it needs to be near an outlet at the right height for whichever gas matters most in your home, which can be a real constraint in an older house with awkward outlet placement.
• No interconnect capability found in the documentation reviewed. Like the Kidde C3010 in this dataset, this appears to be a standalone unit, not designed to link with other alarms.
• The certification claim, however specific, is still the manufacturer's own statement. See "Safety and certification" below.
• Identity nuance worth knowing: the spec sheet we found for this product family is printed under catalog number GCO1B, describing base "Model GCO1" -- the same base model the Amazon listing's GCO1CN designation appears to belong to (First Alert, like Kidde, sells the same base alarm under multiple catalog/SKU codes). We did not find a document confirming GCO1CN is byte-for-byte identical to GCO1B, though everything found points to them sharing the same base design.

Who should choose it

• A household that wants both combustible-gas and CO detection in one plug-in unit instead of buying and mounting two separate alarms.
• Anyone who specifically wants a digital display showing which hazard triggered, rather than a light-only indicator.

Who should skip it

• Anyone who needs battery-only (non-plug-in) placement flexibility -- this unit requires AC power, with battery only as backup.
• Anyone building an interconnected whole-home alarm system -- no interconnect feature was found in the documentation for this model.

Safety and certification

What First Alert states: the engineering spec sheet for this alarm family states plainly that "Model GCO1 has been fully tested and complies with[,] UL1484, UL2034 and other agencies that model their codes after the above agencies" (comma placement as printed in the source document), and separately, "Listing: Listed to UL1484 and 2034 Standards." This is a specific, named-standard claim -- the CO-alarm response-time table on the same document (for example, a 4-15 minute alarm window at a sustained 400 ppm CO concentration) matches the equivalent UL 2034 table found on the Kidde C3010's own spec sheet elsewhere on this site, which is internal consistency worth noting, not proof by itself.

What that is not: as with every other certification claim in this dataset, this is the manufacturer's own documentation, not an independent confirmation by Silent Home Hazards against UL's own certification records. We have not queried UL's listing database for this exact model, so the claim stays unconfirmed by this site.

Sources

• First Alert / BRK "CO & Explosive Gas Combo Alarm" engineering spec sheet (manufacturer, PDF, catalog GCO1B / base Model GCO1) -- supports: sensor types, the UL 1484/2034 listing claim and CO response-time table, dimensions, operating range, mounting-height guidance, warranty.
• First Alert's product page (manufacturer) -- supports: general product description and digital-display feature description (Phase 2.1 research; this page states no certification claim, which the spec sheet above supersedes with a specific one).
• Amazon's product listing for this ASIN -- identity/availability context only; the affiliate link below is generated automatically, not hand-typed.

No customer review text, star rating, or Amazon-listing safety claim was used as a source for any statement in this review.

About this review

Silent Home Hazards has not tested this device firsthand -- we have not installed, alarmed, or measured this unit ourselves. Every specification and claim above is drawn from First Alert's own published materials, cited above, and is written as a sourced claim rather than a first-hand finding.