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Guide · Gas detection · Carbon dioxide

Is there a detector for high levels of carbon dioxide? Portable CO2 monitors with an infrared sensor, colorimetric CO2 tubes, CO2 apps, how accurate a CO2 detector is, how to check one works, where to put one, how to calibrate it

Yes. A portable CO2 monitor with an infrared (NDIR) sensor reads carbon dioxide directly in parts per million or percent by volume, alarms at a set point, and is the instrument for breweries, wineries, dry-ice handling, fermentation rooms, confined spaces and any place CO2 is stored or made; the MSA ALTAIR 5X takes an IR CO2 sensor (0.5 percent low and 1.5 percent high alarms as MSA ships it) and the Honeywell BW Solo is sold in a CO2 version. The other ways people ask about, colorimetric tubes, badge-style color indicators and phone apps, measure something different or nothing at all, and this page sorts them out. The NIOSH limits for CO2 are a 5,000 ppm TWA with a 30,000 ppm STEL and a 40,000 ppm IDLH.

Bayshore Safety. Industrial safety and PPE supplier since 2017. · Current as of November 2026 · NIOSH Pocket Guide to Chemical Hazards, carbon dioxide (CAS 124-38-9; REL, PEL and IDLH as printed); MSA ALTAIR 5X FAQ (0802-85-MC) and ALTAIR 5X operating manual (10150945 r02, factory-set thresholds); Honeywell BW Solo datasheet (Rev C) and Honeywell’s colorimetric tubes pages (automation.honeywell.com, fetched Nov 10 2026); 29 CFR 1910.146 (current eCFR)
CO2 monitors, sensors and calibration gas we stockGas detection selector
BW Technologies BWS1-BL-Y Solo CO2 Monitor, WirelessBW Technologies BWS1-BL-Y Solo CO2 Monitor, WirelessHoneywell BW sells the Solo single-gas detector in a CO2 version; the datasheet gives a 2-month typical battery for the 1S CO2 sensor
$638.40See the product

Why the CO2 question is different from the CO question. Carbon monoxide is a trace toxic gas measured in parts per million with a cheap electrochemical cell, which is why every hardware store sells a CO alarm. Carbon dioxide is present in all air at about 400 ppm, harms at thousands of ppm and kills at a few percent, and an electrochemical cell cannot read it well; MSA’s ALTAIR 5X FAQ puts it plainly: "CO2 is a toxic gas that is difficult to detect with electrochemical sensors", which is why the CO2 sensor in a portable monitor is an infrared one. That difference drives most of the questions below: whether a detector exists, whether a phone can do it, what the colorimetric indicator is, and why a "CO2 reading" from a home device may be an estimate rather than a measurement. The exposure limits themselves are on the CO2 limits guide linked below; this page is about the instruments.

The questions, one by one

Figures are from the NIOSH Pocket Guide, the MSA ALTAIR 5X FAQ and manual, and the Honeywell BW Solo datasheet and colorimetric tube pages.

Is there a detector for high levels of carbon dioxide?Yes, and the right one depends on the level. For work exposure (thousands of ppm to a few percent) the instrument is a portable monitor with an infrared CO2 sensor: the MSA ALTAIR 5X with its IR CO2 sensor reads to 10 percent by volume and ships with alarms at 0.5 percent (5,000 ppm, the NIOSH and OSHA 8-hour limit) low and 1.5 percent high, and the Honeywell BW Solo CO2 is the single-gas version. For a fixed room (a walk-in cooler with dry ice, a fermentation cellar, a CO2 cylinder store) a fixed IR transmitter with a relay does the same job continuously. For indoor air quality (hundreds to 2,000 ppm) the small desk monitors with an NDIR sensor read the same gas at the low end of the scale. What does not detect high CO2 is a carbon monoxide alarm, a smoke alarm, or a phone.
Do they make CO2 detectors, and do carbon dioxide detectors really work?They do, and an infrared one works because the measurement is physical: CO2 absorbs infrared light at a specific wavelength, the sensor measures how much of a lamp’s light reaches the detector through the sample, and the loss is the concentration. MSA’s FAQ describes why the IR sensor is the choice for CO2 and for inert-gas sampling (it needs no oxygen to work and is not poisoned by silicones or lead compounds the way a catalytic sensor is). The instruments in the band are bump tested with CO2 calibration gas like any other sensor, which is the proof that one is working; the daily bump test is the manufacturers’ answer to "how do I check it".
What is the difference between a CO2 detector and a carbon monoxide detector?Different gas, different sensor, different scale. A CO detector reads carbon monoxide (CO, the product of incomplete burning) in parts per million with an electrochemical cell and alarms at tens of ppm (35 or 25 ppm low on the Honeywell BW and MSA units). A CO2 detector reads carbon dioxide (CO2, the product of complete burning, fermentation and breathing) with an infrared sensor and alarms at thousands of ppm or a fraction of a percent. A CO alarm does not see CO2, and a CO2 monitor does not see CO; the 4-gas monitors in the band read CO as one of their four, and the ALTAIR 5X can add CO2 as a fifth.
Is there a CO2 detector app?Not one that measures. A phone has no gas sensor, so an app can only display what a separate Bluetooth CO2 sensor sends it, estimate CO2 from something else (a room’s size and the number of people, or a connected building system), or show a reading from a public air-quality feed. An app that claims to read CO2 from the phone alone is reading nothing. The portable monitors in the band log their own readings; MSA’s ALTAIR io units sync to the MSA Grid cloud and Honeywell BW’s Flex and Ultra pages list Bluetooth options, which is the honest version of "an app for CO2".
What is a colorimetric CO2 detector, and why doesn’t it turn yellow?Two things share the name. In medicine a colorimetric CO2 detector is a disposable paper indicator clipped to an airway that turns from purple to yellow when exhaled CO2 passes over it, to confirm a breathing tube is in the windpipe; it reads breath, not room air, and if it stays purple there is no exhaled CO2 reaching it (or it is spent or wet). In industry a colorimetric CO2 detector tube is a glass tube filled with a reagent that changes color along its length in proportion to the CO2 drawn through it by a hand pump; Honeywell lists colorimetric tubes on its portables page with a pump that draws 50 and 100 cc samples, and the Draeger tube pages on this site cover the same method. Neither is a continuous monitor with an alarm.
What is the most accurate CO2 detector, and are CO2 detectors accurate?For a work atmosphere the accurate instrument is the infrared sensor in a calibrated monitor, because its reading is a direct absorption measurement that is bump tested against a known gas; the ALTAIR 5X manual prints its CO2 performance specification by range, and the sensor is spanned with a CO2 calibration gas. Colorimetric tubes are spot readings with a tolerance printed by the tube manufacturer; low-cost indoor-air monitors vary with their sensor and whether they self-calibrate to outdoor air. We do not rank products; the figure that matters is the one the manufacturer prints, which the rows in the band link to.
How do I calibrate my CO2 detector?With CO2 calibration gas through the instrument’s calibration path, the same two steps as any other sensor: a zero (in air with the normal 400 ppm of CO2, which the instrument treats as its baseline, or in nitrogen where the manual calls for it) and a span with a cylinder of a known CO2 concentration. The ALTAIR 5X manual’s zero and span procedure is the one for that instrument, with a demand flow regulator on the pump inlet; the Honeywell BW Solo CO2 is calibrated through IntelliDoX or its test cap. The CO2 cylinders and kits in the band are the gases; a daily bump test with the same cylinder is how you check the sensor between calibrations.
What is a good CO2 reading in ppm, and what level sets off a CO2 detector?Outdoor air is about 400 ppm and a well-ventilated room a few hundred above that; the NIOSH REL and OSHA PEL are 5,000 ppm as an 8-hour average, NIOSH adds a 30,000 ppm STEL, and 40,000 ppm (4 percent) is immediately dangerous to life or health. A work monitor is set accordingly: MSA ships the ALTAIR 5X CO2 sensor at 0.5 percent (5,000 ppm) low and 1.5 percent (15,000 ppm) high. Indoor-air monitors flag far lower numbers (1,000 to 2,000 ppm) as a ventilation warning, which is a comfort and air-quality figure, not an exposure limit.
Where should you not put a CO2 detector, and how many do you need?A fixed CO2 sensor goes low, near the floor and near the source, because CO2 is about 1.5 times as dense as air and pools in cellars, pits, tank bottoms and cooler floors; it should not go high on a wall, in a draft, next to a door or vent, or where it will be hosed down. A personal monitor goes on the collar in the breathing zone and travels with the worker, so the count is one per entrant plus the pumped unit for the pre-entry test. For a fixed installation the count is one per room or zone where CO2 can collect, placed by the ventilation design; the manufacturer’s installation guide sets the spacing, and a confined space with CO2 is a permit space under 1910.146 whatever the fixed sensors say.
How long does a CO2 monitor last, and what batteries do they take?The infrared sensor has no consumable chemistry, so the limit is the instrument and its battery: the ALTAIR 5X runs on its rechargeable pack for at least 20 hours at room temperature as its page states and its CO2 sensor is replaced as a module; the Honeywell BW Solo CO2 is listed with a 2-month typical battery for the 1S CO2 sensor (the IR sensor draws far more than an electrochemical one, against 12 months for the Solo’s other gases) and a replaceable battery. Fixed transmitters are line powered.
Does humidity affect CO2 levels, and what is the color of CO2?Humidity does not change the amount of CO2 in the air, but water vapor can affect an infrared sensor’s reading if the instrument does not compensate for it, which is why the manuals give an operating humidity range (the ALTAIR 5X: 15 to 90 percent non-condensing). Carbon dioxide has no color and no odor at the concentrations that harm, which is the whole reason for a detector; the white cloud around dry ice is condensed water, not the gas.
Are carbon monoxide and carbon dioxide detectors the same, and what is a normal CO2 level on a monitor?No; see the CO-versus-CO2 card above. A normal reading on a work monitor in open air is about 0.04 percent (400 ppm), which many instruments display as 0.0 percent at their resolution; a reading that climbs toward 0.5 percent in a cellar or cooler is the signal to ventilate before entry.

CO2 detection in plain words

  • A CO2 detector exists: a portable or fixed monitor with an infrared (NDIR) sensor. The MSA ALTAIR 5X and the Honeywell BW Solo CO2 are the ones in these two lines.
  • A CO alarm does not read CO2; the gases, sensors and scales are different.
  • A phone cannot measure CO2; an app only displays a separate sensor or an estimate.
  • A colorimetric CO2 detector is a breath indicator (medical) or a hand-pump tube (industrial); neither is a continuous alarm.
  • Limits: 5,000 ppm 8-hour (NIOSH REL and OSHA PEL), 30,000 ppm STEL (NIOSH), 40,000 ppm IDLH. MSA ships the 5X at 0.5 and 1.5 percent.
  • Mount fixed sensors low and near the source; wear personal monitors in the breathing zone; calibrate with CO2 gas and bump test daily.
NIOSH Pocket Guide (carbon dioxide); MSA ALTAIR 5X FAQ and manual; Honeywell BW Solo datasheet. Fetched Nov 10 2026.

Questions people ask

Is there a detector for high levels of carbon dioxide?

Yes: a monitor with an infrared CO2 sensor, portable (MSA ALTAIR 5X, Honeywell BW Solo CO2, the RKI units in the band) or fixed; it reads CO2 directly and alarms at a set point.

Is there a CO2 detector app?

No app measures CO2 by itself; a phone has no gas sensor. An app can only show a connected sensor’s reading or an estimate.

What is a colorimetric CO2 detector?

A reagent that changes color with CO2: a medical breath indicator that turns yellow, or an industrial hand-pump tube that stains along its length. Neither alarms continuously.

Do they make CO2 detectors?

Yes; the infrared ones in the band, and fixed transmitters for rooms where CO2 is stored or made.

Do carbon dioxide detectors really work?

An infrared sensor measures CO2 directly by light absorption and is bump tested with known gas, so yes; what people doubt is usually a CO alarm or an app that cannot read CO2 at all.

What is the difference between a CO2 detector and a carbon monoxide detector?

Different gases (CO2 from complete burning and breathing, CO from incomplete burning), different sensors (infrared against electrochemical) and different scales (percent against ppm).

What is the most accurate CO2 detector?

We do not rank them; a calibrated infrared monitor reads within the specification its manufacturer prints, and the ALTAIR 5X manual prints that specification.

How many CO2 detectors do you need?

One personal monitor per worker in the atmosphere plus a pumped unit for testing before entry; for a fixed system, one sensor per room or zone where CO2 can collect, placed low.

Where should you not put a CO2 detector?

High on a wall, in a draft, by a door or vent, or where it gets wet; CO2 pools low, so the sensor goes low and near the source.

Why doesn’t the colorimetric CO2 detector turn yellow?

No exhaled CO2 is reaching it, or the indicator is spent or wet; it reads breath, not room air.

Are CO2 detectors accurate?

Infrared monitors are, to the printed specification, when zeroed and spanned with CO2 gas; tubes and low-cost indoor monitors carry wider tolerances.

How to check if a CO2 detector is working?

Bump test it with CO2 calibration gas and watch the reading and the alarm; a fixed sensor gets the same test through its calibration port on the schedule its manual sets.

What is the color of CO2?

None; it is colorless and odorless, which is why a detector is needed. Dry-ice fog is condensed water.

How do I calibrate my CO2 detector?

Zero it in clean air (or nitrogen where the manual says), then span it with a CO2 cylinder through the calibration cap or pump inlet; the ALTAIR 5X procedure is in its manual, and the CO2 kits are in the band.

What is a good CO2 reading in ppm?

About 400 ppm outdoors and a few hundred above that in a ventilated room; 5,000 ppm is the 8-hour limit and 40,000 ppm is IDLH.

What level sets off a CO2 detector?

The set point: MSA ships the ALTAIR 5X CO2 sensor at 0.5 percent low and 1.5 percent high; indoor-air monitors flag 1,000 to 2,000 ppm as a ventilation warning.

How long does a CO2 monitor last?

The IR sensor has no consumable chemistry; the Solo CO2’s typical battery is 2 months and the ALTAIR 5X runs at least 20 hours per charge, as their pages state.

Does humidity affect CO2 levels?

Not the amount of CO2, but water vapor can affect an uncompensated IR reading, which is why manuals give a humidity range.

What batteries do CO2 detectors take?

The Solo CO2 has a replaceable battery; the ALTAIR 5X a rechargeable pack; fixed transmitters are line powered.

Related guides

Carbon dioxide exposure limits and CO2 monitorsPEL, REL, IDLH and the ppm scaleCarbon monoxide exposure limit at workOSHA, NIOSH and the alarm pointsThe four types of gas detector sensorsAnd how to read a 4-gas meterHow to calibrate and bump test an MSA ALTAIR 5XZero, span, the pump test and the sensor-life warningWhat are the alarm set points on a gas monitor?H2S, CO, O2 and LEL defaults as BW and MSA ship themWhat is a confined space?The OSHA definition and permit spaces

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