CO detector

A CO detector is a carbon monoxide sensing device that reports to a control unit rather than sounding on its own, and in Canada it is listed to CAN/ULC-S588, the gas and vapour detector and sensor standard, currently designated CAN-ULC-588-2024A. It is not the device Ontario's codes actually require: both the Fire Code and the Building Code require CO alarms conforming to CSA 6.19 or UL 2034, which are self-contained appliances with their own sounders. Neither Ontario code requires CO detection to be connected to a fire alarm system, and neither says what signal such a connection should produce. Since O. Reg. 87/25 took effect on 1 January 2026, the Fire Code also requires a CO alarm on each storey without a sleeping area, and in public corridors directly heated by a forced air fuel burning appliance.

Detector or alarm: two different devices

This is the most common error on a Canadian submittal, so start here. A CO alarm is a complete appliance: sensor, electronics and sounder in one enclosure, which is what the codes require in dwelling units. A CO detector is an initiating device with no sounder that reports to a fire alarm control unit or a gas monitoring panel. The split is exactly the same as the one between a smoke alarm and a smoke detector.

	CO alarm	CO detector
Self contained sounder	Yes	No, it reports to a control unit
Residential standard	CSA 6.19, or UL 2034	not applicable
Non residential single station	CAN/ULC-S538	not applicable
System connected standard	not applicable	CAN/ULC-S588, currently CAN-ULC-588-2024A
Named in the Ontario codes	Yes	No

Two designations get mangled constantly. CAN/ULC-S531 is the smoke alarm standard and has nothing to do with carbon monoxide. And CAN/ULC-S588 is not a carbon monoxide standard by title: it covers gas and vapour detectors and sensors generally, and its scope excludes fire alarm control units and residential CO alarms. It is still what the ULC listed addressable CO detectors sold in Canada carry.

What Ontario actually requires

For existing buildings the rules are in Ontario Fire Code, O. Reg. 213/07, Division B, Section 2.16, with maintenance and testing in Subsection 6.3.4. For new construction they are in Ontario Building Code, Division B, Subsection 6.9.3. The trigger in both is a residential or care occupancy containing a fuel burning appliance, a fireplace or flue, or a storage garage, or heated by a forced air fuel burning appliance located elsewhere.

O. Reg. 87/25, in force 1 January 2026, widened the Fire Code requirement. Adjacent to each sleeping area is no longer enough on its own: an alarm is now also required on each storey without a sleeping area, and in public corridors directly heated by a forced air fuel burning appliance, at not more than 25 m spacing. Most municipal pages still describe the older rule. The full breakdown, including power, interconnection and the landlord's testing duties, is in Ontario's carbon monoxide alarm rules.

Note what neither code gives you: a dimension for adjacent to each sleeping area. You get a performance test instead, that the alarm be audible in the sleeping rooms with the intervening doors closed.

When CO ends up on the fire alarm panel

When you find CO detectors on a fire alarm control unit in Ontario, it is because a specification asked for it or the owner wanted the annunciator and the monitoring station to see it. That makes the signal type a design decision recorded in the fire alarm matrix, not a code fact.

In practice CO points on a Canadian panel are configured as supervisory or ancillary rather than fire alarm, because the right response to carbon monoxide is to ventilate and leave by the normal route, not to push people into a stairwell that may be the contaminated space. If the vocabulary is hazy, start with alarm, supervisory and trouble signals.

Do not import the American answer. NFPA 72 has a distinctive CO audible signal and a whole chapter on CO detection, and none of it is a requirement here. We could not verify whether CAN/ULC-S524 or CAN/ULC-S527 mandates a classification for a CO input, or what the annunciator must display, because both are paywalled. Get the signal type, annunciation and matrix behaviour written into the specification and confirmed by the engineer of record before you commission. There is no code default to fall back on.

What goes wrong

A CO detector submitted where the code requires a CO alarm. A system connected detector does not satisfy Section 2.16 on its own.
A CO point programmed as a fire alarm input, which evacuates a building for a condition that calls for ventilation.
Sensor life ignored. CO sensing cells have a service life set by the manufacturer, and the code defers to that end of life date rather than giving you a number.
Parking garage sensors confused with life safety devices. Building Code Article 6.2.2.3 ventilation control sensors are a mechanical system, not part of the fire alarm system and not covered by a CAN/ULC-S537 verification.

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