Where to Install Smoke and Carbon Monoxide Alarms
U.S. Fire Administration and EPA guidance on where smoke and CO alarms go, which types to buy, and when to test or replace them, room by room.
Smoke alarms and carbon monoxide (CO) alarms are among the easiest safety upgrades a homeowner can install, and also among the easiest to put in the wrong place. The U.S. Fire Administration (USFA) and the Environmental Protection Agency (EPA) publish clear placement rules for both. Here is how to turn them into an installation plan for your home.
Smoke alarms: where they go
USFA's placement guidance comes down to three rules:
- Inside and outside each bedroom and sleeping area. USFA notes that a closed door may slow the spread of smoke, heat, and fire, which is why an alarm inside the room matters as well as one in the hallway.
- On every level of the home, including the basement.
- On the ceiling or high on the wall. Check the manufacturer's instructions for the exact best spot for your model.
USFA also recommends interconnected alarms, so that when one sounds, they all sound. That matters most in larger or multi-story homes, where an alarm in the basement may not be heard in a second-floor bedroom.
One installation limit: USFA says only qualified electricians should install hardwired smoke alarms. Battery-powered alarms are a normal DIY job, and USFA notes that some fire departments will install battery alarms at no cost.
Which type of smoke alarm to buy
USFA describes two basic sensor types, ionization and photoelectric, which detect different kinds of fires. Since nobody can predict which kind of fire might start, USFA recommends either:
- Both ionization and photoelectric alarms, or
- Dual-sensor alarms that contain both.
USFA's published price ranges give a sense of the cost:
| Alarm type | Price, per USFA |
|---|---|
| Ionization or photoelectric | $6 and up |
| Dual-sensor | $24 and up |
| With a microprocessor (faster alert, fewer false alarms) | $30 and up |
| Wireless (radio frequency interconnect) | $40 and up |
Alarms with strobe lights or vibration are available for people with hearing loss. Your city, county, or state may require a specific type, so USFA suggests checking with your local fire marshal.
Smoke alarm testing and replacement
USFA's maintenance schedule depends on the power source:
- 9-volt battery alarms: test monthly, replace the battery at least once a year, replace the whole alarm every 10 years.
- 10-year sealed lithium alarms: test monthly, replace the whole unit per the manufacturer's instructions.
- Hardwired alarms: test monthly, replace the backup battery at least once a year, replace the alarm every 10 years.
The 10-year clock runs from the manufacture date, not the install date, so check the date printed on the back of the alarm when you take it down to test.
USFA is blunt about nuisance alarms from cooking or shower steam: never pull the battery. Open a window or door, press the hush button, wave a towel to clear the air, or move the alarm several feet away from the kitchen or bathroom. USFA also notes that when a smoke alarm sounds, you may have less than 2 minutes to get everyone outside.
Carbon monoxide alarms: where they go
CO is the colorless, odorless gas USFA calls the "invisible killer." It forms when a fuel-burning appliance such as a furnace, heater, or generator is not working or vented properly. USFA, citing the Consumer Product Safety Commission, says more than 150 people in the United States die every year from accidental CO poisoning not related to fires.
USFA's placement rule for CO alarms:
- In a central location outside each separate sleeping area, and
- On every level of the home.
EPA's indoor air page repeats the same recommendation from the Consumer Product Safety Commission: CO alarms on each level, outside each sleeping area.
What CO alarms can and cannot replace
An alarm is a backstop, not a fix. EPA's list of common CO sources is a useful checklist of things to maintain:
- Unvented kerosene and gas space heaters
- Leaking chimneys and furnaces
- Back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces
- Gas stoves
- Generators and other gasoline-powered equipment
- Car exhaust from an attached garage
EPA's main prevention steps: keep gas appliances properly adjusted, install and use an exhaust fan vented outdoors over gas stoves, open the flue when using a fireplace, never idle a car in the garage, and have a trained professional inspect, clean, and tune the central heating system (furnace, flues, and chimneys) every year. USFA adds two outdoor checks: run portable generators only outdoors, away from doors, windows, and vents, and keep dryer, furnace, stove, and fireplace vents clear of snow and debris.
For context, EPA reports that average CO levels in homes without gas stoves run from 0.5 to 5 parts per million (ppm), levels near properly adjusted gas stoves are often 5 to 15 ppm, and those near poorly adjusted stoves may reach 30 ppm or higher.
A simple installation plan
- Sketch each floor and mark every bedroom.
- Mark a smoke alarm inside each bedroom, one in the hallway outside each sleeping area, and at least one on every other level, including the basement.
- Mark a CO alarm in a central spot outside each sleeping area and at least one on every level.
- Choose dual-sensor (or paired) smoke alarms, interconnected if possible.
- Write the manufacture date on your plan and set a monthly test reminder.
Key takeaways
- USFA places smoke alarms inside and outside every sleeping area, on every level, on the ceiling or high on the wall, ideally interconnected.
- Use both ionization and photoelectric sensing, either as separate alarms or dual-sensor units.
- Test monthly and replace smoke alarms every 10 years from the manufacture date; hardwired units should be installed by an electrician.
- CO alarms go in a central location outside each sleeping area and on every level.
- An annual professional inspection of fuel-burning heating equipment is EPA's main CO prevention step; the alarm is the backup.