10 - Smoke and Carbon Monoxide Alarms: Types, Locations, Service Life

Episode Overview

Smoke and carbon monoxide alarms save lives—but only if properly installed and functioning. Standards of practice usually require reporting presence/absence only, but understanding these devices helps home inspectors educate clients.

Fire Types and Smoke Alarm Types

Two Fire Types:

1. Flaming fires: Lots of flame, little smoke
2. Smoldering fires: Lots of smoke, little flame

Two Smoke Alarm Types:

Ionization Alarms (Most Common):

• Uses radioactive material to ionize air between sensors
• Smoke disrupts electricity flow, triggers alarm
• Slightly better at detecting flaming fires
• Significantly less responsive at detecting smoky/smoldering fires
• May not activate until too late for smoldering fires
• Higher false alarm rate (cooking, candles)

Photoelectric Alarms (Less Common, Better):

• Shines light above sensor at 90° angle
• Smoke reflects light toward sensor, triggers alarm
• Good at detecting smoky (smoldering) fires
• Slightly less responsive than ionization for flaming fires
• Lower false alarm rate

Smoke Alarm Testing Limitations

Test Button Method:

• May only test sound-producing device
• May NOT test sensor functionality
• Sensor can fail while test button still works
• UL-listed aerosol smoke products available (out of scope for home inspection)
• Do NOT use smoke pens or unlisted devices (may damage alarm)

Alarm Service Life

Smoke Alarms:

• Manufacturers recommend replacement after ≈10 years
• Sensors degrade over time and fail
• Failed sensor = useless alarm (false sense of security)
• Original alarms in older houses may be useless

Carbon Monoxide Alarms:

• Service life: ≈5-7 years (shorter than smoke alarms)
• Combination smoke/CO alarms: CO part may fail before smoke part
• Creates partially functional device
• Alert clients to different service lives

Smoke Alarm Location Requirements

Minimum Locations:

• Each bedroom
• Hallway near bedrooms (interpretation: 10-40 feet)
• Each story (including basements and habitable attics)
• NOT in crawlspaces or uninhabitable attics

Split-Level Houses:

• Alarm required on upper level only if: no door between levels AND upper level <1 full story above lower
• Some jurisdictions require alarm on each level regardless
• Manufacturers usually recommend alarm on each level

Carbon Monoxide Alarm Location Requirements

When Required (New Construction):

• Houses with fuel-burning appliances (includes fireplaces)
• Houses with attached garages

Minimum Locations:

• Near bedrooms
• If bedrooms widely separated or on different stories: Multiple alarms required

Key Takeaways

• Photoelectric alarms better than ionization for most home fires
• Test button may NOT test sensor functionality
• Smoke alarms: 10-year service life; CO alarms: 5-7 years
• Each bedroom + hallway + each story minimum
• Interconnection required (hardwired or wireless)
• False alarms lead to disconnected alarms (useless)

Intro

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This episode is hosted by Charlie Bellefontaine of Chicagoland Home Inspectors

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