System Sensor CO1224TR Carbon Monoxide Detector 6-Wire

System Sensor CO1224TR — round-profile 12/24 VDC system-connected carbon monoxide detector with an electrochemical sensing cell, RealTest functional gas testing, a local 85 dBA sounder, a Form C alarm relay and a Form A trouble relay. The manufacturer describes it as a six-wire, system-monitored detector.

The CO1224TR is the round-footprint member of the CO1224 series, intended for locations where the rectangular CO1224T would be visually obtrusive. It is not a stand-alone CO alarm: it wires to a fire alarm, security or combination control panel so that both a CO event and a detector fault are reported off premises, which is what UL 2075 and NFPA 720 commercial installations require. A Form C alarm relay signals CO and a separate Form A trouble relay reports sensor failure or end of life — under UL 2075 that trouble signal is mandatory. RealTest allows the sensing cell itself to be functionally verified with canned CO rather than only exercising the electronics, and a Test/Hush button silences the sounder for five minutes. An internal ten-year end-of-life timer opens the trouble contact when the cell expires. The base mounts to a single-gang electrical box or directly to a wall or ceiling; drywall anchors are included.

Specifications

Installation notes

• Six wires, not four: the manufacturer’s ordering information and installation manual both describe the CO1224TR as a six-wire system-monitored detector — power, a Form C alarm relay and a separate Form A trouble relay. Listings that call it four-wire understate the terminations required.
• The trouble relay is mandatory: per UL 2075 a trouble signal must reach the panel on CO cell trouble or end of life. Terminating only the alarm contact does not satisfy the listing.
• Placement: on a ceiling keep the detector at least 12 inches from any wall; on a wall mount it at least as high as a light switch and at least six inches below the ceiling. Install per NFPA 720, which since 2009 covers both commercial and residential applications.
• Ten-year replacement is absolute: the electrochemical cell has a finite life and is not field-replaceable on this model. When the end-of-life timer expires the trouble contact opens and the whole detector must be replaced. Check the “Replace by” sticker under the cover.
• Hush has a ceiling: Test/Hush silences the sounder for five minutes while the red LED keeps flashing, but hush will not operate above 350 ppm CO.
• RealTest is a gas test: hold Test/Hush for two seconds to enter RealTest, spray canned CO agent, then verify sensing at the panel; the detector exits automatically after roughly 20–60 seconds. Confirm with the AHJ whether a functional gas test is required.
• Altitude: the data sheet states testing to 12,000 feet above sea level for the CO1224T specifically. For high-altitude work verify the CO1224TR’s rating with the manufacturer rather than assuming it carries over.
• Environmental limits are narrow: 32°F–104°F and 22–90% RH, ordinary indoor locations only. Garages and attics are generally outside that range.

Related models

• CO1224T — the rectangular version of the same six-wire system-monitored detector with RealTest; 3.3″ W × 1.3″ H × 5.1″ L, tested to 12,000 ft above sea level
• CO1224A — Canadian model, ULC listed to CSA 6.19-01
• CO-PLATE — replacement plate covering the footprint of previously installed competitive CO detectors on a retrofit

Specifications taken from the manufacturer data sheet “CO1224 Series Carbon Monoxide Detectors with RealTest Technology,” document 9021-60937 Rev. A (2016), and the System Sensor installation and maintenance instructions “CO1224T/CO1224TR Carbon Monoxide Detector,” document I56-3111-012. Manufacturer specifications are subject to change without notice.