· by Michael Blair, Nashville's Electrician
Detector rules are one of the places where the building code and an older house meet. Davidson County now works to the 2024 International Residential Code: Metro’s release on the new codes says the Council gave BL2025-898 final passage in July 2025 and that it applies to plans and applications submitted after July 16, 2025. How much of it reaches the rest of a house when you add a bedroom or finish a basement is something Metro Codes settles on your permit, and we would rather ask than guess. Where the alarms belong is worth knowing either way, whether or not an inspector ever visits.
Where do smoke alarms go in a house?
The U.S. Fire Administration’s smoke alarm guidance puts an alarm in every bedroom, one outside each separate sleeping area, and at least one on every level of the home, the basement included. It says to mount them on the ceiling or high on the wall and to follow the manufacturer’s instructions for the exact spot. We keep them back from the kitchen and the bathroom doors, where cooking smoke and shower steam cause nuisance alarms.
USFA also recommends interconnected alarms, so that when one sounds, they all sound. That is the part older houses tend to miss. It points out that a closed door may slow the spread of smoke, heat and fire, which is good for the person behind it and also the reason the bedroom gets an alarm of its own: a single unit at the far end of the hall can be a long way from someone asleep with the door shut. We run hardwired, interconnected alarms as part of our lighting and outlet work, and in a house that is being rewired we pull the alarm circuit while the walls are open.
Carbon monoxide alarms
The EPA’s page on carbon monoxide and indoor air passes on the Consumer Product Safety Commission’s advice to have CO alarms on each level of the home, outside each sleeping area. The Tennessee State Fire Marshal’s Office carbon monoxide tips give the same placement, a central spot outside each sleeping area and on every level, and add that interconnecting the CO alarms gives the best protection. A combination smoke and CO unit in the hallway saves a device, but it does not replace the smoke alarm each bedroom needs.
The EPA’s list of household sources is a long one: furnaces and gas water heaters that back-draft, wood stoves and fireplaces, gas ranges, generators and other gasoline-powered equipment, and exhaust from an attached garage. A house with none of those has fewer ways to make CO, but a portable generator running during an outage is still one of them, which is why we would put alarms on each level anyway. If you are weighing a generator, our post on generators and transfer switches covers the safe way to connect one.
- Smoke alarm in each bedroom and outside each sleeping area
- Smoke alarm on every level, basement included
- CO alarm on each level, outside the sleeping areas
- Smoke alarms interconnected, so one sets off the rest
What triggers the current rules in an existing house
Not every job does, and the answer for yours belongs to the codes office that issues the permit. Metro’s adopted codes list includes both the 2024 International Residential Code and the 2024 International Existing Building Code, each with local amendments. Adding a bedroom, finishing a basement or attic, or a remodel that opens walls are the jobs where we ask at plan review what alarm work the permit will carry, because that costs far less than finding out at the final inspection.
Outside Davidson County the edition can differ. The State Fire Marshal’s Office code adoption history lists the 2018 International Residential Code as the statewide residential minimum, so before work on a house in Franklin or Murfreesboro we check which edition that city enforces. Where the walls stay closed, wireless alarms that pair with each other by radio can link an older house without fishing cable through every ceiling; whether they satisfy a particular permit is the inspector’s call, so we ask before we quote them. To have us look at your house and tell you what we would put where, ask for a free estimate.
How often should smoke alarms be replaced?
USFA is direct about it: smoke alarms do not last forever, and they need to be replaced 10 years from the manufacture date. Take one down and look for that date before deciding anything. A unit past ten years comes out even if its test button still sounds, because the rule is the age of the whole alarm, not whether it beeps. For CO alarms, go by the replacement date in the manufacturer’s instructions.
USFA describes three kinds of power: a disposable 9-volt battery, a sealed 10-year lithium-ion battery, and hardwired alarms, which usually carry a backup battery that needs replacing once a year. For a house that is not being rewired, the sealed ten-year units are the sensible choice, with no battery to forget. Hardwired alarms are the better install when the walls are already open, and USFA says only qualified electricians should install them.
Sources
- U.S. Fire Administration (FEMA), Smoke alarms — Alarms in every bedroom, outside each sleeping area and on every level; ceiling or high on the wall; interconnection; closed doors slow smoke; replace 10 years from the manufacture date; 9-volt, 10-year lithium-ion and hardwired alarms with a backup battery; qualified electricians for hardwired alarms
- U.S. EPA, Carbon Monoxide’s Impact on Indoor Air Quality — CPSC recommendation of CO alarms on each level outside each sleeping area; household CO sources including attached garages and generators
- Tennessee State Fire Marshal’s Office, Safety Tips on Carbon Monoxide Awareness Day (2018) — CO alarms in a central location outside each sleeping area and on every level; interconnect CO alarms
- Metro Nashville Codes, Metro Adopts 2024 International Building Codes — BL2025-898 passed July 15, 2025, signed July 16, 2025; applies to plans and applications submitted after that date
- Metro Nashville Codes, Adopted Codes List — 2024 International Residential Code and 2024 International Existing Building Code adopted with local amendments
- Tennessee State Fire Marshal’s Office, Codes Enforcement History — Statewide residential minimum is the 2018 International Residential Code
FAQ
Smoke and CO Detectors: What Code Expects Here — questions
Do I need a smoke alarm in every bedroom?
The U.S. Fire Administration recommends one in every bedroom, one outside each sleeping area and at least one on every level, basement included. Whether an existing house has to be brought up to that depends on the permitted work and on what Metro Codes or your local codes office requires, but it is the layout to aim for regardless, because a closed bedroom door can slow smoke on its way to a hallway alarm.
Where should a carbon monoxide detector go?
On each level of the house, outside each sleeping area, which is what the EPA passes on from the Consumer Product Safety Commission and what the Tennessee State Fire Marshal’s Office recommends. Gas appliances, fireplaces, wood stoves and an attached garage are all sources. A combination smoke and CO alarm in the hall still leaves each bedroom needing its own smoke alarm.
How do I interconnect smoke alarms without rewiring?
Wireless interconnected alarms pair with each other by radio, so when one senses smoke they all sound, with no cable between them. They are the practical way to link alarms in an older house where the walls are closed. Whether they meet the requirement on a particular permit is a question for Metro Codes or your local codes office, so it is worth asking before the work starts.
What smoke detectors do I need?
Interconnected alarms, placed in every bedroom, outside each sleeping area and on every level. For a house that is not being rewired we suggest sealed 10-year lithium-ion units, which leave no battery to forget. Where the walls are open, hardwired alarms with a backup battery are the better install, and USFA says a qualified electrician should put them in.