Best CO2 Monitors for Home: NDIR Sensors Only
The best home CO2 monitors, all with true NDIR sensors rather than estimated eCO2: Aranet4, Airthings Wave Enhance, Qingping Air Monitor Lite and more.
Affiliate disclosure: product links on this page go to Amazon, or to the maker's own store for brands that sell only direct. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you; a link to a maker's store earns us nothing. No retailer or brand sees our picks before they are published or has any say in them. How we choose.
The best CO2 monitor for most homes is the Aranet4. It uses a non-dispersive infrared (NDIR) sensor, which measures carbon dioxide directly, shows the reading on an e-ink screen, and runs for years on two AA batteries: Aranet's datasheet gives about 4 years with Bluetooth off at a 5-minute interval, and about 2.8 years with Bluetooth on. For a cheaper monitor that also reads VOCs, noise and light, the Airthings Wave Enhance has an NDIR CO2 sensor that Airthings rates at plus or minus 50 ppm plus 5%.
Indoor CO2 comes mostly from people breathing, so it rises in closed rooms and falls with ventilation, which makes it a practical gauge of whether a bedroom, office or classroom is getting enough fresh air. It is not a pollutant at typical home levels in the sense that PM2.5 is, but high readings mean stale air. The essential buying rule: only buy a monitor with an NDIR sensor. Some cheaper devices display "eCO2" estimated from a VOC sensor, which does not measure CO2 at all.
Our top picks at a glance
1. Best CO2 monitor
Aranet4 HomeCO2 sensor: NDIR (Aranet) · Also measures: Temperature, humidity, pressure · Power: 2 AA, about 2.8 to 4 years (Aranet datasheet) · Display: E-ink with color-coded CO2
2. Best for bedrooms
Airthings Wave EnhanceCO2 sensor: NDIR, ±50 ppm ±5% (Airthings) · Also measures: VOC, humidity, temperature, pressure, noise, light · Power: 2 AA, 14 to 17 months · Display: Color indicator; full readings in app
3. Best CO2 plus particles on a budget
Qingping Air Monitor LiteCO2 sensor: Not named on the listing · Also measures: PM2.5, PM10, temperature, humidity · Power: USB-C, 7-hour battery · Display: OLED with numbers
4. Best all-in-one with CO2
Airthings View PlusCO2 sensor: NDIR (Airthings) · Also measures: Radon, PM2.5, VOC, humidity, temperature, pressure · Power: 6 AA, up to 2 years, or USB-C · Display: E-ink, customizable
| Pick | CO2 sensor | Also measures | Power | Display | Buy |
|---|---|---|---|---|---|
| Aranet4 HomeBest CO2 monitor | NDIR (Aranet) | Temperature, humidity, pressure | 2 AA, about 2.8 to 4 years (Aranet datasheet) | E-ink with color-coded CO2 | Amazon |
| Airthings Wave EnhanceBest for bedrooms | NDIR, ±50 ppm ±5% (Airthings) | VOC, humidity, temperature, pressure, noise, light | 2 AA, 14 to 17 months | Color indicator; full readings in app | Amazon |
| Qingping Air Monitor LiteBest CO2 plus particles on a budget | Not named on the listing | PM2.5, PM10, temperature, humidity | USB-C, 7-hour battery | OLED with numbers | Amazon |
| Airthings View PlusBest all-in-one with CO2 | NDIR (Airthings) | Radon, PM2.5, VOC, humidity, temperature, pressure | 6 AA, up to 2 years, or USB-C | E-ink, customizable | Amazon |
Best CO2 monitor
Aranet4 Home
A dedicated NDIR CO2 monitor with an e-ink screen and battery life measured in years.
- CO2 sensor
- NDIR (Aranet)
- Also measures
- Temperature, humidity, pressure
- Power
- 2 AA, about 2.8 to 4 years (Aranet datasheet)
- Display
- E-ink with color-coded CO2
Pros
- Readable at a glance
- Portable for checking room by room
- Optional buzzer alert
Cons
- No particles or VOCs
- Phone app keeps 90 days of history
Because it runs on batteries for years, the Aranet4 can move from bedroom to office to car without a cable, which is the best way to find out which rooms in your home are under-ventilated. Its color coding and large CO2 number make it easy for anyone in the house to use.
Best for bedrooms
Airthings Wave Enhance
NDIR CO2 with VOCs, humidity, noise and light, in a small battery-powered unit for a nightstand or wall.
- CO2 sensor
- NDIR, ±50 ppm ±5% (Airthings)
- Also measures
- VOC, humidity, temperature, pressure, noise, light
- Power
- 2 AA, 14 to 17 months
- Display
- Color indicator; full readings in app
Pros
- Noise and light help explain poor sleep
- No cable
- Optional free 5-year warranty
Cons
- No on-screen numbers
- Sold on Amazon by a third party when we checked
Airthings pitches the Wave Enhance for bedrooms because CO2 builds up overnight with the door closed. Its noise sensor, Airthings says, takes a reading every six seconds and does not record audio. See our Wave Enhance review.
Best CO2 plus particles on a budget
Qingping Air Monitor Lite
CO2 and PM2.5 with strong independent particle results, refreshing every second.
- CO2 sensor
- Not named on the listing
- Also measures
- PM2.5, PM10, temperature, humidity
- Power
- USB-C, 7-hour battery
- Display
- OLED with numbers
Pros
- AQ-SPEC PM2.5 field R² 0.85 to 0.93
- HomeKit support
- Low price
Cons
- Qingping's listing does not name the CO2 sensor type
- Needs to stay plugged in
If you want both stuffiness and particles on one screen for little money, the Qingping covers both, with one of the better independent PM2.5 results in AQ-SPEC's summary. Check Qingping's spec sheet for the CO2 sensor if NDIR is a must. See our review.
Best all-in-one with CO2
Airthings View Plus
NDIR CO2 alongside radon, PM2.5 and VOCs, for one monitor that covers everything.
- CO2 sensor
- NDIR (Airthings)
- Also measures
- Radon, PM2.5, VOC, humidity, temperature, pressure
- Power
- 6 AA, up to 2 years, or USB-C
- Display
- E-ink, customizable
Pros
- Covers radon and particles too
- Battery or USB power
- Five-year warranty with registration
Cons
- Expensive for CO2 alone
- 7-day sensor calibration
If you also want radon and PM2.5, the View Plus saves buying three devices. See our View Plus review.
How we chose CO2 monitors
Every pick measures CO2 with an NDIR sensor, as each maker states, except the Qingping, whose listing does not name its sensor type; we include it for its particle performance and say so. We favored monitors you can read at a glance and move between rooms, because the main use of a CO2 monitor is finding which rooms need more ventilation.
CO2 buying guide
What the numbers mean
Outdoor air is a little over 400 ppm of CO2. Indoors, levels rise with people and fall with ventilation. ASHRAE says its indoor air quality standards do not use indoor CO2 values to determine acceptable indoor air quality; figures like 1,000 ppm are used as indicators of how well a space is ventilated, not as thresholds of harm. As a practical guide:
| CO2 | What it suggests | What to do |
|---|---|---|
| About 400 to 800 ppm | Well ventilated, close to outdoor air | Nothing |
| 800 to 1,000 ppm | Moderate; typical of an occupied room | Fine for most uses |
| 1,000 to 1,500 ppm | Stuffy; ventilation is not keeping up with occupants | Open a window or door, run a fan |
| Above 1,500 ppm | Poorly ventilated, common in closed bedrooms overnight | Increase ventilation |
Our guide to why CO2 matters at home explains where these numbers come from.
NDIR versus eCO2
An NDIR sensor shines infrared light through a small chamber and measures how much CO2 absorbs. An "eCO2" reading is a guess from a metal-oxide VOC sensor, based on the idea that people emit both; it can be wildly wrong when, say, cleaning products or cooking raise VOCs. If a monitor's specs do not say NDIR, assume eCO2.
Calibration
Many NDIR sensors calibrate themselves by assuming they see outdoor-level CO2 at some point each week. If the monitor never sees fresh air, for example in a room that is never aired, readings can drift. Take it outside or near an open window occasionally, or use the manual calibration if the monitor offers one.
Purifiers do not lower CO2
Air purifiers remove particles and, with carbon, some gases; they do not remove CO2. Only ventilation does. A CO2 monitor tells you when to open a window even if the purifier is running.
What to skip
- Monitors that list eCO2 or "CO2 equivalent".
- CO2 monitors sold as carbon monoxide alarms. They measure different gases; you need a separate CO alarm.
- Treating 1,000 ppm as a danger line. It is a ventilation indicator.
For a budget e-ink monitor that adds particles and VOCs, see our Temtop M10+ review.
Frequently asked questions
What is the best CO2 monitor for home?
The Aranet4: it uses an NDIR sensor, shows CO2 on an e-ink screen and runs on batteries for up to four years. The Airthings Wave Enhance adds VOCs, noise and light for bedrooms.
What is a good CO2 level indoors?
Outdoor air is a little over 400 ppm; indoors, under about 800 to 1,000 ppm suggests good ventilation. ASHRAE's standards do not use CO2 to define acceptable indoor air; higher readings mean the room needs more fresh air.
What is the difference between NDIR and eCO2?
NDIR measures CO2 directly by infrared absorption. eCO2 is an estimate from a VOC sensor and can be badly wrong; buy NDIR if CO2 matters to you.
Do air purifiers reduce CO2?
No. Purifiers remove particles and some gases; only ventilation lowers CO2.
Why is CO2 high in my bedroom at night?
People exhale CO2, and a closed bedroom with little ventilation lets it build up overnight. Opening a window or door, or running ventilation, brings it down.
Is a CO2 monitor the same as a carbon monoxide detector?
No. Carbon dioxide (CO2) and carbon monoxide (CO) are different gases. A CO2 monitor does not protect against carbon monoxide; fit a separate CO alarm.
Sources
- Aranet4 HOME, Aranet
- Airthings Wave Enhance product sheet, Airthings
- View Plus product sheet, Airthings
- How Much Ventilation Is Enough? Aim for 5, CDC, National Institute for Occupational Safety and Health
- AQ-SPEC Sensor Evaluations: Summary of PM Sensors, South Coast Air Quality Management District
- Datasheet Aranet4 HOME, Aranet
- Indoor Carbon Dioxide, Ventilation and Indoor Air Quality (issue brief), ASHRAE
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Airthings View Plus Review: Radon, PM2.5 and NDIR CO2 in One Monitor
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