Horn

A horn is an audible signal device, the appliance that produces the tone occupants hear when the fire alarm system operates. Ontario's Building Code never names horns, bells or speakers separately. Article 3.2.4.18 sets sound pressure levels that any audible signal device has to deliver at the occupant rather than at the device: not less than 10 dBA above ambient and not less than 65 dBA within a floor area with intervening doors closed, and not less than 75 dBA in a sleeping room in a building of residential occupancy. In a sleeping room in a residential or care occupancy Sentence 3.2.4.18.(6) requires a low frequency signal, which an ordinary horn does not produce.

Last updated: September 2026

Horn, bell or speaker, and why the Code does not care

Ask three technicians what goes on the wall and you will get horns, bells and speakers. Ask the Building Code and you get one term, audible signal device, used throughout Article 3.2.4.18 without distinguishing between them.

That is deliberate. The Code writes a performance requirement, so the obligation attaches to the sound arriving at a person, not to the technology that made it. A horn, a bell, a horn-strobe and a speaker on a tone are all compliant devices if the level at the occupant clears the threshold, and all non-compliant if it does not.

The practical effect is that you cannot answer a code question by pointing at a data sheet. A 95 dBA rating is measured at a reference distance under laboratory conditions. What the Code asks about is the far corner of a furnished room with the door shut.

What the horn has to achieve

Location	Level	Sentence
Within a floor area	Not less than 10 dBA above ambient and not less than 65 dBA	3.2.4.18.(7)
Sleeping room, residential occupancy	Not less than 75 dBA	3.2.4.18.(5)
Suite smoke detectors installed in lieu of smoke alarms	Between 75 dBA and 110 dBA within the individual suite	3.2.4.20.(10)(a)

All of the floor area and sleeping room figures are measured with any intervening doors closed. The maximum permitted level is the messy part of the article and is set out honestly in fire alarm audibility in Ontario, because the printed text of Sentence 3.2.4.18.(4) contradicts itself.

Pattern, not just volume

A fire alarm signal is a pattern as well as a level. For smoke alarms, Sentence 3.2.4.20.(16) requires the sound pattern either to meet the temporal patterns of alarm signals, or to be a combination of a temporal pattern and a voice relay.

For the fire alarm system itself, the Building Code does not print the pattern. The definition of the alarm signal, the alert signal and the timing that distinguishes them lives in CAN/ULC-S524, which is paywalled. What the Code does regulate is what those signals mean in a two-stage building, which is covered in single-stage versus two-stage.

Silencing a horn inside a dwelling unit

City of Markham Builder Tip No. 67, written to the 2024 Ontario code, quotes Sentence (8): an audible signal device located within a dwelling unit shall include a means for it to be manually silenced for a period of not more than 10 min.

Sentence (12) offers automatic signal silence as an alternative where the in-suite devices are on separate circuits, subject to conditions that catch people out. Silence cannot occur within the first 60 s of operation, or within the zone of initiation. A subsequent alarm elsewhere in the building must reactuate the silenced devices. After not more than 10 min the devices must return to a continuous signal if the alarm has not been acknowledged. And any voice communication system must be able to override the automatic silence.

Where a horn is the wrong device

Two situations rule a plain horn out. In a sleeping room in a residential or care occupancy, the device has to emit a low frequency signal. And in the spaces listed in Article 3.2.4.19, sound alone is not accepted at all and a strobe is required in addition.

Beyond that, horns are the ordinary case, they draw less current than strobes, and they are usually what sets the baseline for audibility across a floor.

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