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Smoke & Carbon Monoxide Alarm Placement — Where the Code Puts Them

Smoke alarm placement in a dwelling is a fixed list: each bedroom, outside each sleeping area, and every story. Carbon monoxide alarms attach to the same permit triggers whenever the home has fuel-fired appliances or an attached garage.

Requirement	Model Code Standard	Section
Smoke alarms — in bedrooms	One in each sleeping room	IRC R314.3
Smoke alarms — outside bedrooms	One outside each separate sleeping area, in the immediate vicinity of the bedrooms	IRC R314.3
Smoke alarms — every story	At least one per story including basements and habitable attics	IRC R314.3
Interconnection & power	Hardwired with battery backup and interconnected so all sound together; listed wireless interconnection allowed	IRC R314.4, R314.5
CO alarms — where	Outside each separate sleeping area, and required when the dwelling has fuel-fired appliances or an attached garage; in bedrooms when a fuel-fired appliance is in the bedroom or its bathroom	IRC R315.2, R315.3
Alterations trigger	Interior alterations, repairs, or additions requiring a permit bring the whole dwelling up to smoke/CO alarm requirements (battery-only allowed where no wiring access)	IRC R314.2.2, R315.2.2
Kitchen/bath spacing	Ionization alarms not within 20 ft of a permanent cooking appliance (10 ft with a silencing feature); photoelectric alarms not within 6 ft; not within 3 ft of bath doors with tub/shower	IRC R314.3.1

Worth knowing

The alterations trigger surprises homeowners: a simple permitted remodel means alarms in every bedroom of a 1970s house.
NFPA 72 governs installation details the IRC references — ceiling placement, distance from walls, and sloped-ceiling rules come from there.
Many states layer their own CO statutes on top of the IRC, including rental-property requirements.
Combination smoke/CO units are permitted and are the practical answer for the outside-sleeping-area location.

Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.

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