System Sensor CO1224T — 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 CO1224T is not a stand-alone CO alarm. It is designed to be wired to a fire alarm, security or combination control panel so that a CO event and a detector fault are both reported off premises, which is what UL 2075 and NFPA 720 commercial installations require. Power comes from the panel or an auxiliary supply, an alarm relay signals CO, and a separate supervised trouble relay reports sensor failure or end of life — under UL 2075 that trouble signal is mandatory, not optional. RealTest allows the sensing cell itself to be functionally verified with a canned CO agent rather than only exercising the electronics, and the 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
| Model |
CO1224T (US only) |
| Sensing technology |
Electrochemical CO sensing cell |
| Wiring |
Six-wire, system monitored |
| System voltage |
12/24 VDC nominal; minimum 10 VDC, maximum 33 VDC |
| Average standby current |
20 mA |
| Maximum alarm current |
40 mA (75 mA in test) |
| Maximum start-up capacitance |
20 µF |
| Alarm relay |
Form C, 30 VDC @ 0.5 A |
| Trouble relay |
Form A, 30 VDC @ 0.5 A |
| Audible signal |
85 dBA minimum at 10 ft, ANSI temporal 4 pattern |
| Operating temperature |
32°F to 104°F (0°C to 40°C) |
| Operating humidity |
22 to 90% RH |
| Altitude |
Tested up to 12,000 ft above sea level |
| Alarm thresholds |
Alarms within the times specified by ANSI/UL 2034 at 70, 150 and 400 ppm CO |
| Sensor life |
Approximately ten years; built-in end-of-life timer opens the trouble contact |
| Dimensions |
3.3″ W × 1.3″ H × 5.1″ L (84 × 33 × 130 mm) |
| Weight |
7 oz (198 g) |
| Input terminals |
14 to 22 AWG, SEMS screws |
| Mounting |
Single-gang back box, or surface mount to wall or ceiling |
| Listing |
UL 2075, Gas and Vapor Detectors and Sensors |
| LED — normal standby |
Green blinks once per minute; red off |
| LED — alarm |
Red blinks in temporal 4 pattern; sounder in temporal 4 |
| LED — RealTest mode |
Green blinks once per second |
| LED — CO trouble |
Red blinks once per minute; green off |
| LED — end of life |
Both LEDs off |
Installation notes
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Six wires, not four: the CO1224T is a six-wire system-monitored detector — power, a Form C alarm relay and a separate Form A trouble relay. Listings that call it a four-wire device understate the terminations required. Plan conductor count and panel zones accordingly.
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The trouble relay is mandatory: per UL 2075 a trouble signal must be sent to the panel on CO cell trouble or end of life. Wiring only the alarm contact and leaving the trouble contact unterminated does not meet the listing.
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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 down from the ceiling. Install per NFPA 720; since 2009 that standard covers both commercial and residential applications, and the commercial chapter calls for detectors on the ceiling in the same room as permanently installed fuel-burning appliances and centrally on every habitable level and in every HVAC zone.
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Ten-year replacement is absolute: the electrochemical cell has a finite life. Check the “Replace by” sticker under the cover; when the timer expires the trouble contact opens and the whole detector must be replaced, not just cleaned.
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Hush has a ceiling: the Test/Hush button silences the sounder for five minutes and the red LED keeps flashing, but the hush function will not operate above 350 ppm CO.
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RealTest is a gas test, not a button test: hold Test/Hush for two seconds to enter RealTest, spray canned CO agent, then verify sensing at the panel. The detector exits RealTest automatically after roughly 20–60 seconds. Confirm with the AHJ whether a functional gas test is required for the installation.
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Environmental limits are narrow: 32°F–104°F and 22–90% RH. Do not install in garages, attics or other spaces that fall outside that range, and note this is an ordinary indoor location product.
Related models
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CO1224TR — the round-footprint version of the same six-wire system-monitored detector with RealTest; 6.0″ diameter, 11 oz
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CO1224A — Canadian model, ULC listed to CSA 6.19-01
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CO-PLATE — replacement plate that covers the footprint of previously installed competitive CO detectors during 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.
