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How many smoke alarms are required in an Ontario home?

Last updated: June 2026

Short answer: Smoke alarms are required on every storey and outside sleeping areas, interconnected so all sound when one detects smoke.

Detailed explanation

Part 9 requires smoke alarms on each storey of a dwelling unit and in proximity to bedrooms. Interconnection ensures occupants on all levels are alerted.

New work typically requires hardwired alarms with battery backup. CO alarms are required near sleeping areas when fuel-burning appliances or an attached garage are present.

Secondary suites need alarms that warn occupants in both the suite and the main dwelling.

Relevant OBC sections

  • Ontario Building Code

    Section 9.10.19. — Smoke alarms

  • Ontario Building Code

    Section 9.33.4. — Carbon monoxide alarms

Example scenario

You have one battery alarm on the main floor of a two-storey home. Adding alarms on the second floor and basement, interconnected, brings the house up to current requirements.

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