Home Self-Reliance Shelter Fire & Utility Safety Smoke Alarms & CO Detectors

Shelter · Fire & Utility Safety

Smoke alarms and CO detectors. A household reference.

Where to place them, how to test and maintain them, what each alarm means, and what to do when each type sounds. Sourced from NFPA 72.

Smoke alarms CO detectors Maintenance schedule

Two different devices

They detect different hazards. The distinction matters.

Smoke alarms and CO detectors are frequently confused, sometimes combined, and occasionally treated as interchangeable. They are not. Each detects a distinct threat, has distinct placement requirements, and requires a distinct response when it activates.

Smoke Alarm

What it detects: Airborne combustion particles produced by fire — either visible smoke or invisible particles from a flaming fire.

The threat it addresses: House fires. The alarm provides early warning that gives occupants time to escape before conditions become unsurvivable.

Placement principle: High — heat and smoke rise. Ceiling or high on wall (at least 4 inches from ceiling if wall-mounted).

When it sounds: Get out. Do not investigate. Follow your escape plan.

Replaces at: 10 years from manufacture date (check inside the unit).

CO Detector

What it detects: Carbon monoxide — an odorless, colorless gas produced by the incomplete combustion of fuels (gas, oil, wood, propane).

The threat it addresses: CO poisoning. CO accumulates in enclosed spaces and is lethal at high concentrations. It cannot be detected by human senses.

Placement principle: CO is approximately the same density as air, so placement at various heights is acceptable. Follow manufacturer guidance — typically breathing height (around 5 feet) or ceiling.

When it sounds: Get everyone out immediately. Call 911 from outside.

Replaces at: 5-7 years (check manufacturer specifications — shorter lifespan than smoke alarms).

Combination smoke/CO alarms

Combo units detect both threats in a single device. They are a reasonable choice for most households — particularly where limited outlets or space makes separate units difficult. When buying a combo unit, confirm both sensors meet current standards: the smoke sensor should be dual-sensor (ionization + photoelectric, or just photoelectric for sleeping areas), and the CO sensor should be electrochemical. Not all combination units pair equal-quality sensors.

Smoke alarms

Placement, types, and the test button.

The placement requirements below come directly from NFPA 72, the National Fire Alarm and Signaling Code — the standard referenced by most local building codes.

Where to place them (NFPA 72)1

Required locations

Inside every bedroom — one per sleeping room
Outside every sleeping area (in the hallway serving bedrooms)
Every level of the home, including the basement
On the ceiling or high on a wall (at least 4 inches from ceiling if wall-mounted)

Avoid placing near

Within 10 feet of a cooking appliance (reduces false alarms from steam and cooking smoke)
Peaked ceiling apex — install 4 to 12 inches down from the peak
Windows, doors, or HVAC vents where drafts may interfere with detection
Bathrooms — steam activates ionization alarms

How many is enough: A typical three-bedroom, two-story home with a basement needs a minimum of six alarms. Larger homes or homes with multiple sleeping areas need more. When in doubt, add rather than subtract — the cost of an additional alarm ($10-30) is trivial relative to its function.

Ionization alarms

Faster at detecting fast-flaming fires. More prone to nuisance alarms from cooking. Best suited for areas away from kitchens.

Photoelectric alarms

Faster at detecting slow, smoldering fires — the type most likely to produce fatalities because they develop overnight while occupants sleep. NFPA and USFA recommend photoelectric or dual-sensor alarms for sleeping areas.

Dual-sensor alarms

Contain both ionization and photoelectric sensors. Provide the widest detection coverage. The recommended type for sleeping areas and any home where simplicity is preferred.

Interconnected alarms: why they matter

When alarms are interconnected, triggering any one alarm sounds all of them throughout the home. This is especially important in multi-story homes, large homes, or any home where a fire starting in the basement could develop significantly before reaching the sleeping-area alarm.

In the scenario that matters most — a smoldering fire that starts while everyone is asleep — an interconnected system ensures that an alarm in the kitchen or utility room activates the alarm in the bedroom before dangerous conditions reach the sleeping area.

Hardwired interconnect

Alarms connect through the home's wiring. Most reliable; requires an electrician for retrofit in existing homes. Standard in new construction.

Wireless interconnect

Alarms communicate via radio frequency or WiFi. Practical retrofit for existing homes. No wiring required. Look for models that specify wireless interconnect capability.

Smart alarms with app notification

Send alerts to your phone when an alarm sounds — useful for vacation properties or when traveling. Not a substitute for a hardwired or wireless interconnect at home.

When the smoke alarm sounds: what to do

1

Get out immediately. Do not stop to get dressed, gather belongings, or investigate the source of the alarm.

2

Before opening any door: touch it with the back of your hand. A hot door means fire is on the other side — use your secondary exit (the window).

3

Get low if there is smoke in the hallway. Smoke and heat accumulate at ceiling level; cleaner air is lower.

4

Go to the meeting point outside. Account for everyone in the household.

5

Call 911 from outside. Give your address clearly.

6

Never re-enter a burning building for any reason. Emergency responders are trained and equipped for this; household members are not.

1 NFPA 72: National Fire Alarm and Signaling Code, current edition. National Fire Protection Association.   2 Ahrens, Marty. "Smoke Alarms in U.S. Home Fires." NFPA Research, 2021.   3 U.S. Fire Administration. "Smoke Alarms in U.S. Residential Fires." USFA Topical Fire Research Series, 2019.

Carbon monoxide detectors

The invisible gas. The one alarm you cannot skip.

Carbon monoxide is produced whenever fuel — gas, oil, wood, propane, charcoal — burns incompletely. It is odorless, colorless, and indistinguishable from normal air without a detector. Roughly 400 people die from unintentional, non-fire CO poisoning in the U.S. each year.4

Where to place CO detectors

Required locations

At least one detector on each level of the home
Outside every sleeping area (so the alarm wakes you)
Near any fuel-burning appliance: furnace, water heater, gas range, fireplace
On the same level as, or directly adjacent to, an attached garage

Placement notes

CO is approximately the same density as air — any height is acceptable, unlike smoke alarms
Follow manufacturer guidance — typically recommends breathing height (5 feet) or ceiling mounting
Avoid windows, doors, and HVAC vents where drafts may affect sensor accuracy
Not inside the garage itself — CO detector belongs in the adjacent living space

Common CO sources

Gas furnace and water heater

Most common source of home CO. A cracked heat exchanger or blocked flue vent can produce significant CO without any visible sign.

Vehicles in an attached garage

Running a vehicle even briefly in an attached garage — including with the garage door open — can produce CO levels that penetrate the living space.

Portable generators

The most common cause of acute CO poisoning deaths during power outages. CPSC: never run inside a garage, basement, or any enclosed space — including with doors open.5 20+ feet from any window, door, or vent.

Fireplaces and wood stoves

Blocked or damaged chimney flues can cause CO to back-draft into the living space. Annual chimney inspection is recommended for any wood-burning appliance.

Gas and charcoal grills

Never use inside or in an attached structure, even with ventilation. CO accumulates quickly in enclosed spaces.

Fuel-burning heaters and camp stoves

Propane, kerosene, or other fuel-burning heaters are for outdoor use only. Using them indoors during a power outage is a documented cause of CO deaths.

Symptoms of CO exposure

CO symptoms are frequently mistaken for flu — but without fever. Multiple household members experiencing the same symptoms simultaneously is a strong indicator of CO exposure.

Headache (most common early symptom)

Dizziness, weakness, or confusion

Nausea or vomiting

Shortness of breath or chest pain

Symptoms that improve when leaving the building

Pets behaving unusually or showing distress

If symptoms improve when outside: This pattern — worse inside, better outside — is a classic CO poisoning indicator. Do not return inside. Call 911 and seek medical evaluation even if symptoms seem mild. CO can cause serious effects without being immediately obvious.

When the CO alarm sounds

1

Get everyone out immediately, including pets. Do not stop to investigate.

2

Leave a door open as you exit to help ventilate the space.

3

Call 911 from outside. Tell them a CO alarm is activated.

4

Do not re-enter until emergency responders have inspected the building and cleared it.

5

Seek medical attention if any household member has headache, dizziness, nausea, or weakness — even mild symptoms.

4 CDC. "Carbon Monoxide Poisoning." Centers for Disease Control and Prevention (cdc.gov/niosh/topics/co).   5 CPSC. "Generator Safety." Consumer Product Safety Commission (cpsc.gov). See also: CPSC Safety Alert 5114.

Testing and maintenance

The schedule. Both devices.

A smoke alarm with a failed battery or a CO detector past its service life is not a working alarm. The maintenance schedule for both devices is simple — the difficulty is making it a consistent habit.

Device

Monthly

Annually

Replace entire unit

Smoke alarm (battery)

Standard or 9V battery unit

Press test button — should sound clearly

Replace battery. Test after replacing.

10 years from manufacture date (check inside the unit)

Smoke alarm (10-year sealed)

Non-replaceable sealed battery

Press test button — should sound clearly

No battery to replace — test button confirms function

10 years from manufacture date — the sealed battery and alarm reach end of life together

CO detector (battery)

Standard or 9V battery unit

Press test button — should sound clearly

Replace battery. Test after replacing.

5-7 years. Check manufacturer — CO detectors have a shorter sensor lifespan than smoke alarms

Combo smoke/CO alarm

Combined detector

Press test button — confirms both sensors

Replace battery if not sealed. Confirm both functions sound.

Follow the shorter of the two lifespans (typically 5-7 years for the CO sensor, or as the manufacturer specifies)

Testing correctly

Press the test button on the alarm — this is the correct test. The button tests the alarm's complete circuit, including the sounder and the sensor electronics.

A smoke alarm with a green status light but no response to the test button is faulty and should be replaced immediately.

An alarm that chirps briefly every 30-60 seconds (not a full alarm) is indicating low battery or end-of-life status — this is the alarm asking to be serviced, not a false alarm.

Never test a smoke alarm by holding a lit match near it to generate smoke — this doesn't test the electronics and can leave residue that reduces sensor sensitivity over time.

Finding the manufacture date

The manufacture date is stamped inside every alarm, typically on the back of the unit or inside the battery compartment. It looks like "Date of Manufacture: MM/YYYY" or similar phrasing.

Smoke alarms more than 10 years past this date should be replaced regardless of whether they appear to function normally. The sensor sensitivity degrades with age.

CO detectors typically have a shorter lifespan — 5 to 7 years is common, though some manufacturers specify 10 years. Check the documentation or the label inside the unit.

If an alarm in your home has no visible manufacture date, treat it as end-of-life and replace it.

What to buy

The devices worth buying once and maintaining.

Each product slot below matches the device category to a specific recommendation. Prioritize photoelectric or dual-sensor smoke alarms for sleeping areas. Confirm any CO detector uses an electrochemical sensor.

Affiliate disclosure: New World Survival earns a small commission on purchases made through links on this page, at no cost to you. We only recommend gear we'd put in our own home.

Related guides

Connect this page to the full section.

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The complete guide: escape plans, bedroom doors, fire drills, and common fire causes. This page provides the alarm reference detail.

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Gas shutoff procedures — relevant when a CO alarm suggests a gas appliance issue or leak.

Generator and Backup Power Safety

Generator placement, distance requirements, and the CO risk that makes this the leading cause of outage-related deaths.

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The room-by-room inspection that surfaces alarm placement gaps and batteries that need replacing.
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