The short version: put a smoke alarm inside every bedroom, outside each sleeping area, and on every level of your home, including the basement. Carbon monoxide (CO) alarms go in similar spots, near bedrooms and on each floor. Mount them on the ceiling or high on a wall, and follow your alarm’s instructions and local rules.
Where you put smoke and CO detectors matters almost as much as owning them. Let’s go through it room by room, then cover how often to test and replace them.
Where should smoke detectors go in your home?
Standard guidance, including what fire safety groups recommend, is to install smoke alarms in these places:
- Inside every bedroom
- Outside each separate sleeping area, such as in the hallway
- On every level of the home, including the basement
- In the basement, on the ceiling near the bottom of the stairs leading up
Why so many? Because fire can start anywhere, and you want the alarm to reach you while you’re asleep behind a closed door. Interconnected alarms, where one sounds all of them, make this even safer.
How high should you mount a smoke alarm?
Smoke rises, so alarms belong high. A ceiling mount is usually best, and NFPA guidance says to keep the alarm at least 4 inches from the nearest wall. If you’re using a wall, place the alarm high, with the top edge between 4 and 12 inches below the ceiling.
That 4-inch gap matters because dead air space in the corner where the wall meets the ceiling can keep smoke from reaching the sensor. Your alarm’s instructions may add other distances, so follow them too.
Where should you not install smoke alarms?
Placement mistakes cause a lot of false alarms, and people who get fed up sometimes take the batteries out. That’s dangerous. So where should you avoid? Keep alarms away from:
- Kitchens and cooking appliances, since steam and cooking smoke can set them off. NFPA guidance says to keep them at least 10 feet from cooking appliances.
- Bathrooms with showers, where steam can trigger them.
- Vents, fans and windows, where drafts disturb airflow.
- Very hot or very cold spots, like unfinished attics, unless the alarm is rated for them.
If a kitchen alarm keeps going off while you cook, move it or use a model with a hush button, but never disable it.
Where should carbon monoxide detectors go?
CO is invisible and odorless, so an alarm is your only warning. NFPA guidance calls for CO alarms on every level of the home, including the basement, and outside each sleeping area, close to the bedrooms. Homes with an attached garage or fuel-burning appliances, like a furnace, gas stove or fireplace, especially need one.
CO mixes with air fairly evenly, so follow your manual on whether the alarm goes on a wall or ceiling. Don’t mount it right beside a fuel-burning appliance, since brief puffs at startup can cause false alarms, and don’t put one in the garage itself. Also avoid blocking it with furniture or curtains, and plug-in models need an outlet that isn’t switched off or covered.
Combination alarms and smart detectors
You can buy separate smoke and CO alarms or a combination unit that does both. Combination units save wall space and simplify upkeep. If you like that idea, our guide to the best smoke and carbon monoxide detectors walks through the choices.
Smart versions can send a notification to your phone if you’re away and tell you which room triggered the alarm. Take a look at our roundup of the best smart smoke detectors with carbon monoxide detection to see what features are out there. Just remember that a smart alarm still has to sound locally, so the loud siren is what matters most.
Testing and replacing your detectors
A detector in the right spot only helps if it works. Make this a habit:
- Test every alarm monthly by pressing the test button.
- Replace batteries when the alarm chirps, or on the schedule in your manual. If a new battery doesn’t stop the chirp, the alarm may be at the end of its life.
- Replace the whole smoke alarm about every 10 years.
- Replace CO alarms on the timeline the maker lists, often 7 to 10 years, and sooner if the alarm signals end of life.
Most alarms print the manufacture date on the back, so check it. And while you’re protecting your home, a leak is another common hazard. Our guide to the best water leak detectors with a shutoff valve is a good next read.
Alarms are one piece of a connected home. If you’d like to build on that, our smart home starter guide is a friendly place to begin.
Frequently asked questions
How many smoke detectors do I need?
You need one in each bedroom, one outside each sleeping area and one on every level. A bigger home with many rooms will need more than a small apartment.
Can I use one detector for both smoke and carbon monoxide?
Yes. Combination alarms detect both, as long as the label says so and the unit is listed by a testing lab such as UL. Follow its placement rules, and don’t use a smoke-only alarm as a substitute for CO protection.
Should smoke alarms go on the ceiling or the wall?
Either can work if mounted correctly. A ceiling is usually the best location, at least 4 inches from any wall, and a wall mount should sit 4 to 12 inches below the ceiling. Check your manual for exact distances.
The bottom line
Good smoke and CO detector placement is simple: cover every bedroom, every sleeping area and every floor, mount high, and keep alarms away from steam and cooking. Test monthly and replace old units on schedule. When in doubt, check your alarm’s manual and your local fire code.