Carbon monoxide has no color, no smell, and no taste. Nothing in your senses will tell you it is in the room, which is why placement of a detector is not a decorating decision — it is the only warning you get.
CDC describes CO poisoning as producing symptoms often mistaken for the flu, and reports that several hundred people die each year in the United States from unintentional carbon monoxide poisoning not linked to fires. (Source: CDC, Carbon Monoxide Poisoning Basics.) Published annual figures vary with the year and method, generally falling in the range of roughly 400 to 500 deaths; the number matters less than the fact that the exposure is silent and preventable.
This guide covers where alarms go and why. What to do when one sounds is a separate, urgent question owned by the CO alarm response guide.
Start with the rule that governs everything else
An alarm is a second layer. It warns you that the first layer already failed.
No placement makes it acceptable to run a generator in a garage, use a grill indoors, heat a home with an oven, or operate any outdoor combustion device in an enclosed or partly enclosed space. The generator carbon monoxide warning owns that boundary, and it is not negotiable regardless of how many alarms are installed.
Read the rest of this page with that framing. You are placing a smoke-alarm-equivalent for an invisible gas, not buying permission.
Where alarms belong
CPSC’s core guidance is short and specific: install CO alarms on each level of the home and outside sleeping areas. More precisely, CPSC recommends one alarm in the hallway outside the bedrooms in each separate sleeping area. (Source: CPSC, CO Alarms.)
That produces a practical baseline:
- One outside each separate sleeping area. A home with bedrooms at two ends of the house has two sleeping areas, and therefore two alarms — not one in the middle.
- One on every level, including a finished basement that contains a sleeping area.
- Near or over an attached garage, where vehicle exhaust is a common source.
- Interconnected where possible, so an alarm at one end of the house is heard at the other. CPSC notes interconnected alarms provide broader warning when one activates.
Guidance commonly places an alarm within about 10 feet of each bedroom door. Follow your specific alarm’s instructions, which take precedence over any general rule of thumb.
Height: why the smoke-alarm intuition is wrong
People often assume CO sinks or rises, and place the alarm accordingly. Both intuitions are unhelpful.
CO mixes well with the air in a house. CPSC notes CO alarms may be installed into a plug-in receptacle or high on the wall, because CO from any source will be well-mixed with the room air. (Source: CPSC, CO Alarms.)
The practical consequence: height is far less important than being in the right room and being audible. A plug-in unit at outlet height outside a bedroom is doing its job. Do not skip an alarm because you cannot mount it at a particular height, and do not relocate one to a worse room to achieve a better height.
Follow the manufacturer’s instructions for the specific model — some units have their own height and clearance requirements.
Where alarms do not belong
CPSC advises against installing CO alarms in attics or basements unless they include a sleeping area. (Source: CPSC, CO Alarms.) Beyond that, avoid locations that cause false alarms, dead sensors, or missed warnings:
- Directly above or beside a fuel-burning appliance, where normal brief startup emissions can trigger nuisance alarms.
- In humid areas such as directly in a bathroom, where moisture affects some sensors.
- In direct sunlight, near vents, fans, or open windows, where air movement can dilute the sample or temperature can affect the unit.
- Behind furniture, curtains, or doors, or anywhere the sound is muffled.
- In an unconditioned space outside the alarm’s stated temperature range.
- Where it cannot be heard from the bedrooms — an alarm nobody wakes up to is decorative.
Check the manufacturer’s exclusions. They are model-specific and more authoritative than any list here.
Audibility is part of placement
A correctly placed alarm that nobody can hear has not been placed correctly.
- Test that it is audible from inside each bedroom with the door closed, at night, over a fan or white-noise machine if one is used.
- Households with hearing loss should use alarms with compatible visual or vibrating alerts. Do not assume a standard sonic alarm will wake everyone.
- Older adults, people who sleep deeply, people who use sleep medication, and children may not wake or may not recognize the alarm. Someone must be responsible for them in a real event.
- Anyone who cannot self-evacuate needs a plan that names who assists them, decided before the alarm sounds.
Renters and apartments
Many jurisdictions require CO alarms in rental housing, and requirements vary. Two practical rules:
- Report a missing, dead, or expired alarm in writing to the landlord or building management and keep a copy. A written request creates a record and is the right escalation path.
- Do not remove, disable, cover, or relocate a hardwired or building-supplied alarm yourself. Battery replacement per the instructions is usually appropriate; anything structural is not.
Where you cannot add hardwired units, a plug-in or battery alarm placed per the manufacturer’s instructions in the right room is a legitimate supplement. Shared-building sources — an attached garage, a neighboring unit, a shared mechanical room — are a management issue, not a resident repair.
A placement worksheet
| Location | Alarm needed? | Installed | Audible from bedrooms? | Notes |
|---|---|---|---|---|
| Outside sleeping area 1 | Yes | |||
| Outside sleeping area 2 (if separate) | Yes | |||
| Each additional level | Yes | |||
| Near attached garage | Yes | |||
| Basement with sleeping area | Yes | |||
| Basement/attic without sleeping area | No per CPSC | — | — | |
| Directly above fuel appliance | No | — | — | Nuisance alarms |
Fill it once, keep it with the household records, and revisit it after any move, renovation, appliance change, or new occupant.
Placement is not maintenance
An installed alarm is not a working alarm. Sensors have a service life, and “the light is on” does not prove the unit is still within it. Testing intervals, battery changes, and end-of-life replacement are their own discipline — see the CO detector testing and replacement schedule.
Placement also does not substitute for maintaining the equipment that produces CO in the first place. Fuel-burning appliance service and venting belong to qualified professionals; the HVAC resilience hub holds those records, and the extreme cold and emergency heating hub covers the cold-weather decisions that tempt households into unsafe heat.
What to do before you buy anything
- Count your separate sleeping areas and levels. That number, not a package deal, sets how many alarms you need.
- Check what already exists, including hardwired units and their manufacture dates.
- Confirm local code and, for renters, lease and landlord obligations in writing.
- Read the intended model’s placement, height, temperature, and exclusion instructions before choosing a spot.
- Place, test for audibility from every bedroom, and record the install and replacement dates.
- Rehearse the response — because the alarm’s whole purpose is the action it triggers.
ReadyLience has not tested any CO alarm and does not recommend a product. Certification, listing, local code, and the manufacturer’s instructions decide what is appropriate for your home.
Sources reviewed
ReadyLience reviewed current carbon-monoxide alarm and information guidance from CPSC, CO poisoning basics from CDC, detector-placement guidance from EPA, and heating-safety guidance from the U.S. Fire Administration. Annual CO mortality is cited as a published range rather than a single precise figure, because reported totals vary by year and method. Placement guidance is general; the specific alarm’s instructions, local code, and property authority control actual installation. Emergency services, utilities, clinicians, and qualified fuel, HVAC, chimney, and electrical professionals control actual response and repair. This page remains in expert review and no product is recommended.