How do CO detecors work? There doesn't seem to be much to the point on the web. I know about the SnO2-based gas detectors. They're power-hungry and not very specific.
Jeroen Belleman
simple DC DC up converter
May 07, 2026
Last reply: 2 months ago
69 Replies
They use a chemical reaction of some sort. Some have a surface that blackens when exposed to CO.
I think the problem is that the reaction is cumulative.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Typically in the EU the electrochemical version is used:
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produce a current into a 'short', e.g. a TIA. A problem is that when the power fails a TIA is not a short, and the cell deteriorates. A depletion mode low-ohmic JFET is sometimes used to short the cell when power fails. Life is about 10 years, so most detectors here come with a fixed 10 year Li battery.
Arie
In the US, we have much the same, including the fixed ten-year life. Usually there is a long list of patent numbers on the detector, and a few of those patents tell the story. The ones here are typically tin oxide based.
Joe
I've decided to go that route...I can get a 1000mAh li for not a lot more than a couple of AAs...just add a charger for a few pence.
The Wikipedia article is short on detail. A NIST site promises in the title to explain how it works, but in the article just skips the issue. My own chemistry knowledge is lacking in this case.
Mmmh. I'd have expected Bill Sloman to chime in here. After all, he's our resident chemistry expert.
I found at winsen-sensor.com some of the answer: CO + H_2 O -> CO_2 + 2H^+ + 2e^- That would be the reaction at the cathode. The 2e^- is the output signal. I didn't think CO would react with water in this way, but what do I know...
I suppose at the anode we then have:
2H^+ + 2e^- -> H_2 .So, water in the detector is consumed and will run out eventually. Hydrogen diffuses into the anode metal or out into the environment. Bill? Did I get that right?
Bare CO sensors are sold by AliExpress: Search for ME2-CO.
Jeroen Belleman
I got a Ph.D. in physical chemistry in 1970. That doesn't make me an expert on today's carbon monoxide detectors.
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You aren't sensing a lot of carbon monoxide. It's a toxic gas and if there is much of it around people die. The air we breathe (and definitely the air we breathe out) contains a lot more water vapour and the sensor shouldn't run out of water.
Hydrogen does diffuse through pretty much everything. Not enough to make it impossible to create pretty high vacuums, as in the proton path around CERN.
The sensors look at the electrode voltages - the sensor is an electrochemical cell.
Norton-symantec doesn't like the web-sites that that search string finds.
Thanks for that link. That was pretty much what I was looking for.
Jeroen Belleman
The measurement is about current, not voltage.
An ME2-CO search finds this one:
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ME2-CO-Ф14*14 carbon monoxide sensor The ME2-CO-Ф14*14 carbon monoxide sensor is a fuel cell sensor. Carbon monoxide and oxygen undergo corresponding redox reactions on the working electrode and counter electrode and release charge to form a current. The current generated is proportional to the concentration of carbon monoxide and follows Faraday's law By measuring the magnitude of the current, the carbon monoxide concentration can be determined. Features: Low power consumption, high precision, high sensitivity, wide linear range, strong anti-interference ability, excellent repeatability and stability. Application: It is widely suitable for the detection of carbon monoxide concentration in commercial, especially civil fields. Parameter: Detection gas: carbon monoxide (CO) Range: 0 ～ 1000ppm Maximum measurement limit: 2000ppm Sensitivity: > 0.8nA / ppm <<=== CURRENT, not VOLTAGE! Resolution: 1ppm Response time (T90): <30S Load resistance (recommended): (500 / 1k / 2k) Ω Repeatability: <3 ﹪ output value Zero drift (-20 ℃ ～ 40 ℃): ≤10ppm Temperature range: -20 ℃ ～ 50 ℃ Humidity range: 15 ﹪ ～ 90 ﹪ RH Pressure range: standard atmospheric pressure ± 10﹪
The diagram:
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a TIA, a 1 kOhm resistor is used to prevent the cell from being open circuited. The circuit measures the output current into a short, not the open circuit voltage.
Arie
No need to copy the whole datasheet. We can find that by ourselves.
Again, as is common for gas detectors, the specificity leaves to be desired. They also detect ethane and hydrogen.
Jeroen Belleman
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