G-4Gas · CO alarms
Carbon monoxide alarms: the rules and the response
Carbon monoxide alarms are required in NYC homes and apartment buildings: the owner installs one within 15 feet of each bedroom door, tenants keep it working, and when it sounds everyone gets out first.
Which building is yours?
- Prewar walk-upThe owner installs the alarm within 15 feet of each bedroom door; you test it monthly, change batteries and repay $25 within a year.
- Brownstone or row houseCity law requires CO alarms in one- and two-family homes too. If you rent out a floor, you install there and the tenant maintains it.
- Co-op or condo high-riseRental units follow the owner-installs rule. For shareholder or owner-occupied units, the board and residents decide who is responsible.
- Two-family houseThe owner installs alarms in both units; the tenant tests theirs, changes batteries and repays $25 for each new or replacement alarm.
- New-build condoA new building needs hard-wired alarms. Who replaces one in an owner-occupied unit is set between the board and the unit owners.
What do you do when a CO alarm sounds?
Get everyone out to fresh air, then call 911 from outside. FDNY puts it simply on its FDNY Smart safety site: "If a CO alarm sounds, you and your family should get out immediately and call 911." You cannot tell from inside whether the alarm is right, so never assume it is a false alarm.
National Grid gives the same order for a suspected leak with no alarm: go outside immediately and report it to 911 (National Grid, Carbon Monoxide). The Health Department lists the early signs as tiredness, nausea, dizziness and headaches. Feeling any of them with no alarm sounding is still a reason to go outside and call 911.
The FDNY video covers both smoke and CO alarms and how they sound. One point to keep straight: for a CO alarm, call 911 from outside; never assume it’s a false alarm, even if it went quiet on its own.
Where must the alarm go?
Owners must install CO alarms within 15 feet of the primary entrance to each sleeping room, in one- and two-family homes and in apartment buildings (NYC311, Carbon Monoxide). FDNY also recommends an alarm on every level, including the basement.
One DOB homeowner page words the placement as "at least 15 feet from bedroom entrances". HPD, 311 and HPD’s required notice all say "within", and that is the rule this site follows.
Who installs, who maintains, who pays?
The owner installs and the tenant maintains. HPD’s page says owners of multiple dwellings and of rented one- and two-family homes with fuel-burning devices must install at least one approved CO detector per unit and replace it at the end of its life (HPD detectors). Tenants test it monthly and replace batteries twice a year. The owner files a certificate of installation within 10 days, according to 311.
The tenant repays the owner $25 for each new or replacement alarm and has a year to pay, as 311 and HPD state it on 11 Nov 2026. A combined smoke and CO unit is $50. HPD says tenants in Class B multiple dwellings pay nothing. A building with no fuel-burning devices and no enclosed parking can be exempt.
Legend: the numbers on this plate
- 15 feetMaximum distance from the alarm to each bedroom’s main entranceNYC311
- $25Tenant repays the owner per CO alarm, with a year to payNYC311
- 10 daysOwner files a certificate of installationNYC311
- MonthlyTenant tests the alarm; batteries changed twice a yearHPD tenant duties
| Building | Who installs | Who tests and changes batteries | Notes |
|---|---|---|---|
| Prewar walk-up | Owner | Tenant | Tenant repays $25 per alarm |
| Brownstone or row house | Owner | Tenant in a rented unit; owner in their own | Required in one- and two-family homes |
| Co-op or condo high-rise | Owner for rental units | Resident | Board and shareholders settle owner-occupied units |
| Two-family house | Owner | Tenant in the rented unit | HPD duties apply when a unit is rented |
| New-build condo | Owner for rental units | Resident | New buildings need hard-wired alarms |
How long does an alarm last?
Until the end of the maker’s stated life. The Admin Code says a CO alarm is replaced when its time in service passes the manufacturer’s suggested useful life, and replacement devices must have an end-of-life signal. FDNY’s page says to replace alarms every 10 years or when that signal sounds. A DOB page says every five years; the code and HPD go by the manufacturer, so go by the life the maker states for your model.
Existing buildings may use battery or plug-in alarms with battery backup. New or substantially improved buildings need hard-wired ones, which matters in a new-build condo.
Is a CO alarm the same as a gas detector?
No. Con Edison says plainly that "a carbon monoxide detector is not the same as a gas leak detector" (Con Edison gas safety). A separate natural gas detector rule starts January 1, 2027, under Local Law 102 of 2025, for multiple dwellings and rented one- and two-family homes with gas piping. If you smell gas, the steps are different and start with leaving without touching anything that sparks: see what to do if you smell gas, and the gas and CO section for the rest.
What if the alarm is missing or broken?
Tell the owner, super or management company in writing. In a rental, a missing CO alarm is the owner’s to fix, and you can call 311 for HPD if it is not installed. A dead battery is the tenant’s to replace, according to HPD and 311.
Questions people ask
The CO alarm stopped after a minute. Do you still need to leave?
Yes. Get everyone out and call 911 from outside. An alarm that goes quiet does not mean the air is safe.
Who pays for a CO alarm in an apartment?
The owner buys and installs it, and the tenant repays $25 per alarm within a year. A combined smoke and CO alarm is $50.
Does a co-op shareholder have to buy their own alarm?
The city leaves that to the board and shareholders in owner-occupied co-ops and condos. Rental apartments in the same building follow the owner-installs rule.
Can a CO alarm warn you about a gas leak?
No. Con Edison says a CO detector is not a gas leak detector. Natural gas detectors are a separate requirement from January 1, 2027.
How often should you test it?
Monthly, by pressing the test button, and change batteries twice a year, as HPD sets out for tenants.
How this plate was drawn
Written from HPD’s detector page, 311’s carbon monoxide article, FDNY Smart, National Grid, Con Edison and the Admin Code’s replacement rule, checked 11 Nov 2026. Some city pages give other first steps or another number to call; we follow FDNY’s order of out first, then 911. The DOB page’s "at least 15 feet" and "five years" wording conflicts with HPD, 311 and the code, so we did not use it. We could not find the text of the original 2004 CO law on a city site.
Sources
- FDNY — Be #FDNYSmart, working smoke and CO alarms (video) · get out and call 911 when a CO alarm sounds; testing monthly · checked 11 Nov 2026
- NYC311 — Carbon Monoxide · placement, certificate, $25 repayment, co-op note · checked 11 Nov 2026
- HPD — smoke, CO and natural gas detector duties · owner and tenant duties, $25 and $50 amounts · checked 11 Nov 2026
- National Grid — Carbon Monoxide · suspected CO, go outside and call 911 · checked 11 Nov 2026
- Con Edison — Gas safety · CO alarm is not a gas detector · checked 11 Nov 2026
Plate G-4 · revised 11 Nov 2026