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

Send us Fan MailEpisode OverviewSmoke 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 TypesTwo Fire Types:Flaming fires: Lots of flame, little smokeSmoldering fires: Lots of smoke, little flameTwo Smoke Alarm Types:Ionization Alarms (Most Common):Uses radioactive material to ionize air between sensorsSmoke disrupts electricity flow, triggers alarmSlightly better at detecting flaming firesSignificantly less responsive at detecting smoky/smoldering firesMay not activate until too late for smoldering firesHigher false alarm rate (cooking, candles)Photoelectric Alarms (Less Common, Better):Shines light above sensor at 90° angleSmoke reflects light toward sensor, triggers alarmGood at detecting smoky (smoldering) firesSlightly less responsive than ionization for flaming firesLower false alarm rateSmoke Alarm Testing LimitationsTest Button Method:May only test sound-producing deviceMay NOT test sensor functionalitySensor can fail while test button still worksUL-listed aerosol smoke products available (out of scope for home inspection)Do NOT use smoke pens or unlisted devices (may damage alarm)Alarm Service LifeSmoke Alarms:Manufacturers recommend replacement after ≈10 yearsSensors degrade over time and failFailed sensor = useless alarm (false sense of security)Original alarms in older houses may be uselessCarbon Monoxide Alarms:Service life: ≈5-7 years (shorter than smoke alarms)Combination smoke/CO alarms: CO part may fail before smoke partCreates partially functional deviceAlert clients to different service livesSmoke Alarm Location RequirementsMinimum Locations:Each bedroomHallway near bedrooms (interpretation: 10-40 feet)Each story (including basements and habitable attics)NOT in crawlspaces or uninhabitable atticsSplit-Level Houses:Alarm required on upper level only if: no door between levels AND upper level <1 full story above lowerSome jurisdictions require alarm on each level regardlessManufacturers usually recommend alarm on each levelCarbon Monoxide Alarm Location RequirementsWhen Required (New Construction):Houses with fuel-burning appliances (includes fireplaces)Houses with attached garagesMinimum Locations:Near bedroomsIf bedrooms widely separated or on different stories: Multiple alarms requiredKey TakeawaysPhotoelectric alarms better than ionization for most home firesTest button may NOT test sensor functionalitySmoke alarms: 10-year service life; CO alarms: 5-7 yearsEach bedroom + hallway + each story minimumInterconnection required (hardwired or wireless)False alarms lead to disconnected alarms (useless)IRC Code ReferencesIRC 2018: R314 (smoke alarms), R315 (carbon monoxide alarms)Intro This episode is brought to you by GetSync.pro This episode is hosted by Charlie Bellefontaine of Chicagoland Home InspectorsFor complete training with visual materials, practice exams, and certification support, visit nhiexamprep.com© 2025 National Home Inspector Exam Prep Podcast. All rights reserved.