CO Alarm Calculator
CO alarm count, placement, and replace date.
What it does
Carbon monoxide kills quietly: colorless, odorless, and mimicking flu before consciousness fades. Alarms outside sleeping areas and on every level buy the wake up that senses cannot.
The tool above takes home levels with sleeping area count. It returns the alarm count, placement rule, and 10 year replacement date.
The default 2 levels with 2 sleeping areas needs 4 alarms retiring 2036. The ranch case of 1 and 1 needs 2.
Fire protection guidance sets the placement: outside each sleeping zone plus every level with basements counted. Consumer safety guidance repeats the layout with monthly testing.
Mount, test, and date every unit, then service fuel burning appliances yearly. Generators stay outside far from windows, cars never idle in garages, and chirps mean replace, not just new batteries.
How to use
- Type the levels.
- Type sleeping areas.
- Read the alarm count first.
- Read placement beside it.
- Read the replace date last.
- Test monthly after mounting.
Formula
- levels
- Stories including basement, 1 to 4.
- areas
- Separate bedroom zones, 1 to 8.
- alarms
- Planning count of alarms.
NFPA alarm guidance places CO alarms outside each separate sleeping area with units on every level including basements. CPSC carbon monoxide guidance mirrors the same placement with monthly testing. Counts here plan coverage; grouped bedrooms can share one hallway unit.
Worked example
Example: two story home
Defaults: 2 levels, 2 sleeping areas.
- Home: 2 levels with 2 sleeping areas.
- Count: 2 + 2 = 4 alarms.
- Place: outside each sleeping area plus every level.
- Life: 10 year sensors from 2026 retire 2036.
- Check: basements and attached garages included.
- Tool shows 4 alarms, Outside each sleeping area + every level, 10 year sensors: replace by 2036.
Reference table
| Home | Count | Retire |
|---|---|---|
| 2 levels, 2 areas | 4 alarms | 2036 |
| 1 level, 1 area | 2 alarms | 2036 |
| 3 levels, 4 areas | 7 alarms | 2036 |
| 2 levels, 1 area | 3 alarms | 2036 |
Limits
- Planning counts, not code sign off.
- Grouped rooms may share units.
- Local codes can exceed this.
- Detectors never fix sources.
Common mistakes
- One alarm for three floors.
- Skipping the basement unit.
- Ignoring end of life chirps.
- Mounting beside fuel appliances.
- Generators near windows.
Try it yourself
Quick checks. Answers sit tucked under each question.
Ranch, 1 level, 1 area?
1 + 1 = 2 alarms with the same placement rule.
3 levels, 4 areas?
3 + 4 = 7 alarms across the plan.
0 levels?
Zero levels is no house: enter 1 to 4 levels.
Questions
Where do alarms go?
Outside each sleeping area plus every level including basements. Attached garages earn their own.
Maintain how?
Monthly tests, dusting, and date checks. End of life chirps differ from low battery beeps.
Poisoning signs?
Headache, dizziness, nausea, confusion at low levels; unconsciousness at high. Leave first, then call 911.
Sources?
Furnaces, water heaters, fireplaces, stoves, generators, and idling cars. Annual servicing cuts risk.
Open windows enough?
No. Detectors alarm; only shutting sources and ventilating clears the gas.
Sealed units?
Yes, sealed 10 year units avoid battery swaps but still expire by date.