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    Root Catalog > Default Category > Solutions & Support > Support > CO Detector FAQs

    Frequently Asked Questions (FAQs) about Carbon Monoxide (CO) Detection with the Carbon Monoxide Inspector


    If your question is not answered below, or if you're still unsure, we encourage you to contact us.




    1. How accurate is the Inspector?
    2. How does the MAX mode work (and when should I use it)?
    3. Do I need a pump? (or why should I buy the kit?)
    4. I'm a property owner, should I mount this on the wall?
    5. Why should I pay more for this when I can get a cheap carbon monoxide detector from Home Depot (most common question from homeowners/general consumers)?
    6. I'm getting a ppm reading, what does it mean/what should I do?
    7. I've used portable CO detectors in the past, what's different about the Inspector?
    8. I'm certain there's no CO around, why am I getting a ppm reading?
    9. I'm confused, what's the difference between Carbon Dioxide (CO2) and Carbon Monoxide (CO)? (Carbon Dioxide (CO2) VS. Carbon Monoxide (CO)





    1. Do I need to calibrate it, and if so, how?
    2. How long does the battery last?
    3. My past experience with gas detectors has included a lot of costly maintenance, how does the Inspector compare




    1. How accurate is the Inspector?

    Very accurate for the price. Every Inspector is calibrated before shipment.  The LCD display has a resolution of 1ppm.  Generally speaking, the accuracy is +/-10%, (e.g. a reading of 100ppm will be displayed when the concentration reaching the sensors is 90-110ppm).  At concentrations lower than 20ppm, the accuracy is +/-2ppm.  The only products out there that are more accurate (well, they claim they are...we have our doubts on some of the products), cost a lot more.Operating the CO Inspector

    2. How does the MAX mode work? (and when should I use it)

    Simply press the MAX button, an arrow over the MAX sign indicates MAX mode is active.Suppose you are curious about the maximum CO level you are exposed to by exhaust from vehicles when you walk down a city block.  If you wear the Inspector with MAX mode active, you'll find out.  Perhaps you wish to sample the exhaust from your chimney, furnace, or hot water heater, the MAX mode is perfect for this, because the concentration will change a lot due to air mixing.  Operating in MAX mode is almost always preferable when you use the hand aspirator pump. Speaking of pumps, in professional applications the norm has been an electronic sampling pump to draw a sample from a remote location (e.g. a confined space).  These pumps, with their high power, cost, and long lengths of tubing are very cumbersome.  In many cases, you can use the MAX mode to eliminate the need for that annoying motorized pump.  By operating in MAX mode, you can simply tie a lanyard or rope to the Inspector clip, and lower the Inspector (or in some cases toss the Inspector) into the area of interest, wait ~1 minute, then pull it back and view the reading.  All this talk about pumps brings us to the next FAQ.

    3. Do I need a pump?

    Not required for ambient measurements, you only need it for drawing remote samples (e.g. from an exhaust stream or reaching the ceiling). You can't shove the Inspector itself into a hot exhaust stream, but you can draw a sample to it with a pump.  Sensorcon sells the CO Inspector Kit, which, in addition to the CO Inspector, includes a robust yet inexpensive carrying case and a hand aspirated pump.  Hand aspirated pumps use rubber bulbs (like your doctor uses for blood pressure testing) to draw an air sample from the end of a stainless steel probe, down a hose, through a filter, and to the Inspector's sensor.  Other applications besides exhaust testing include fast surveying of a building.  With a pump, you can more quickly draw air from the ceiling or behind a stove, or just around you as you walk through a building.  This allows you to quickly assess the CO concentration throughout a large area as you walk through it.  We like using the MAX mode for a lot of these scenarios. Hand Aspirator vs. Motorized PumpsMotorized pumps offer a more steady airflow than the pulses you'll get with a hand aspirator, but motorized pumps consume a lot of power, and cost much more (>10X the price).  With a hand aspirated pump used in combination with the Inspector's MAX mode, you'll be able to perform almost all of the tasks you can do with a motorized pump, at a much lower cost and with less headache.

    4. I'm a property owner, should I mount this on the wall?

    That's not what we had in mind, but you can if you really want to.  Please note that the alarm in the CO Inspector is not nearly as loud as smoke detector style CO detectors. Instead of mounting on the wall, we suggest setting it on your night stand when you are not carrying it around.The Inspector is not like the cheap smoke detector style CO detectors (usually bulky and white).  The CO Inspector is a professional grade portable CO detector, you can carry it, clip it on your clothing, or place it anyplace you want.  The cheap wall mount CO detectors are not as accurate as the Inspector, and most have alarms that won't sound for long periods of time (this is to comply with false alarm standards such as UL2034).  The CO Inspector will alarm immediately when the CO concentration exceeds 35ppm.  This leads us to the next FAQ:

    5. Why should I pay more for this when I can get a cheap carbon monoxide detector from Home Depot (Most common question from homeowners/general consumers)?

    The Inspector is a tool for measuring actual CO concentrations and alarming above 35ppm.  Those cheap CO detectors are only meant to sound an alarm when CO concentrations are elevated for extended periods of time.  (It's like measuring a room with a tape measure vs. just using your eyes, when you're half asleep!)  Table: UL2034 VS. CO Inspector Professional CO Detector

    CO Concentration UL2034 CO Detectors Sensorcon CO Inspector
    0-30ppm Nothing happens from 0-30ppm (it just sits there quietly, looking ugly) Instant readout on LCD display in 1ppm increments
    30-70ppm Probably nothing still! At 30ppm+, there is a small chance that it will alarm, but not for at least 30days! (no joke, look at the UL2034 standard, it says the device is not supposed to alarm for at least 30days at 30ppm. This means it might not ever alarm until it's next threshold of 70ppm) Instant readout on LCD display in 1ppm increments. LED and audible 1st alarm starts instantly at 35ppm+, which corresponds to the 8 hour time weighted average (TWA) set by the National Institute for Occupational Safety and Health (NIOSH)
     70-150ppm  At 70+ppm, alarm supposed to start in 60-240 minutes Instant numerical readout, alarms active
     150-400ppm  At 150+ppm, alarm supposed to start in 10-50 minutes Instant numerical readout, alarms active, higher alarm starts at 200ppm, which corresponds to the 15minute ceiling set by NIOSH.  Ceiling means this is the maximum workers should be exposed to for any period of time.  (in other words, DON'T wait 10-50 minutes!)
     400ppm+  At 400+ppm, alarm supposed to start in 4-15 minutes  Instant numerical readout, high alarms active

    Pros of cheap smoke detector style CO detectors (e.g. Kidde, First Alert, aka those ugly round or square white things!):

    1. Cheap wall/ceiling mount CO detectors have louder buzzers than the CO Inspector.
    2. Conform to UL2034 (the standard that most state laws dictate in the US)
    3. They're cheap.

    Cons of cheap smoke detector style CO detectors (did we mention that they're ugly!): 

    1. Conform to UL2034...what?!... Yes, this is both a pro & con. UL2034 is not a very good standard, as it has a heavy focus on preventing false alarms, so such devices are required to wait long periods before alarming (unlike smoke detectors which will alarm nearly immediately).
    2. Alarm at high concentrations (not supposed to alarm below 30ppm, may or may not up to 70ppm.  The inspector alarms at 35ppm, which is the current 8-hr exposure limit set by OSHA).  Bottom line, if you have health problems or small animals, these cheap alarms may not be suitable for you, they typically say so on the box.

    Using the Inspector as a supplement to cheap CO detectors:

    We're not on a crusade to eliminate cheap CO detectors, they are typically good for sounding an alarm in homes where healthy people live.  The Inspector can be thought of as a supplement, a diagnostic tool.  If you think there might be CO present, but the cheap alarms didn't sound, the Inspector will tell you (i.e., maybe there's a low CO concentration of
    10-20ppm making you tired, if there is, where might it be coming from?).  Unlike the cheap alarms which only alarm after 15minutes (or hours), you can use the inspector to get instant readings. The Inspector is currently in use by many EMTs and fire departments.  HVAC technicians and home inspectors also use the Inspector on maintenance calls.  Bottom line, the Inspector is more expensive than the $20-$50 you'll pay at the big box store, but you'll be getting a professional grade American made instrument, that is easy to use and suitable for giving you real CO concentration information vs. just a delayed alarm.

    6. I'm getting a ppm reading, what does it mean/what should I do?

    At concentrations of <5ppm, you probably don’t need to worry, just keep an eye on it.  At higher concentrations, you need to investigate further.

    Table:  What does a CO reading of X ppm mean?

    ppm Reading Possible Meaning What you should do
    0-5 ppm - CO is normally present in the air at- Electronics Noise (the sensor is accurate to 2ppm) - Keep an eye on it, it’s normal to see small transients  of 1-2ppm. If it stays in the 3-5ppm range, there may be a very small amount of CO present.

    - Concentrations moving between 0 & 2-3ppm are typically sensor noise, typically this happens when the instrument is adjusting to a new ambient temperature.

    *0-4.4 ppm CO is the EPA standard for good air quality (green)

    5-10 ppm - Indoors: there may be a small source of CO in the building.  This is typically caused by a gas stove, cigarettes, an attached garage with an opening into the house, or a furnace or hot water heater with improper venting.

    - Outdoors: Most likely there is a local source of CO, such as a campfire, grill, or automobile exhaust.  In urban environments, such concentrations may be encountered, especially at busy intersections.

    - If indoors, see if you can find elevated levels of CO by walking through the building with the CO Inspector.  For faster evaluation, use the hand aspirator pump to draw samples around you when you walk, squeezing the bulb about once/second.  Keep the Inspector in MAX mode to hold a high reading.

    - If outdoors, pay attention to what’s going on around you to try to identify potential sources.  See if lower concentrations are observed in different locations.

    *4.4-9.4 ppm CO is the EPA standard for moderate air quality (yellow), highly sensitive groups may start to have adverse health issues.

    10-35 ppm - Indoors: these concentrations indicate that there is a local source of CO in the building.

    - Outdoors:  There may be a lot of traffic (cars, motorcycles, ATVs, boats, etc.) around you, or you may be close to a burning fire (camp fire, grill, etc.)

    - Unless you are performing an exhaust test, these concentrations are higher than you should be exposed to over extended periods of time.  If you smell exhaust, you are not smelling CO (CO is odorless) you are smelling other gases such as NOx, but vehicle exhaust has many toxic gases, including CO, NOx, some particulate matter and unburned hydrocarbon fuel. 10s of ppm CO is typical in a garage where a car was recently operating.

    - If indoors, it is again most likely to be coming from combustion processes in the house, like a stove, furnace, hot water heater, fireplace or cigarettes

    *9.5-30.4ppm is the EPA classification for unhealthy to very unhealthy CO air quality.

    35 ppm+ - Indoors:  These concentrations are considered hazardous, and are almost certainly coming from a large leak in a furnace or boiler/hot water heater

    - Outdoors:  You are most likely exposed to heavy traffic or close to the exhaust of 1 or more vehicles

    - NIOSH specifies 35ppm as an 8-hr TWA limit, meaning workers should not be exposed to this time weighted average concentration for more than 8 hours.

    - If you are in an environment with such high levels, you should not stay in this environment very long until the CO source is found and corrected.

    - If you are indoors and the reading is >35ppm, you should immediately ventilate the building and turn off all combustion processes.


    7. I've used portable CO detectors in the past, what's different about the Inspector?

    The Inspector combines a rugged, compact, quality design with excellent ease of use and low cost. Generally speaking, there are 3 kinds of portable CO detectors sold on the market today:

    1.  Diagnostic CO Detectors:  These are usually fairly large devices sold by Bacharach, Fluke, UEI & others.  In most cases they have poor battery life and are not water resistant.  They are fairly easy to use, most have a MAX mode, require occasional calibration, and typically cost $200-$400+.  Diagnostic CO detectors are usually used by home inspectors, HVAC technicians, and fire departments.  Most are actually not made by the company on the label, rather they are made by a Chinese/Taiwan manufacturer who "private labels" for the company marketing the device.  Support for these products is virtually nonexistent, as since the companies that sell them generally don't make them, they are not knowledgeable about their use. Sensorcon's CO Inspector is made to the highest quality in the USA. It is rugged, waterproof, has a standard battery that lasts for years, and is supported by Sensorcon's knowledgeable staff.

    2. Safety CO Detectors: These are compact devices sold mainly by large gas detector companies for $100-$400+, who are only concerned with selling high volumes to large mining or industrial operations.  They require frequent calibration.  For $100-$200 you can get a "disposable" detector, typically with a 2 year life. The cheapest ones don't even display the ppm concentration level on the LCD display, rather they just say something like "24months remaining"! (SARCASM ALERT! Gee whiz, I bought this gas detector, it will only alarm if I'm in a dangerous situation, other than that it just tells me how much longer it will live...good to know!).  For $200-$400 (or more) you can get a serviceable gas detector that allows you to replace the sensor...for $100-$300.  Right now the most popular (high volume) portable CO detectors are the 2-year disposable devices. Sensorcon's CO Inspector is just as small and robust as these safety oriented CO detectors, but much easier to use, without the gimmicks.  Sensorcon's support staff will answer anybody's questions, not just large customers, so if you're a 1 man shop or just an average consumer that wants better information about Carbon Monoxide, we're here for you.

    3.  Carbon Monoxide Analyzer:  If you see the word "analyzer" it usually only means you will pay more, i.e. $450-$1000+, usually for the same technology, but a more fancy High CO Exhaust Readinglooking device.  Maintenance issues (meaning costs) are much higher.  You can use the CO Inspector for almost any application you can use an analyzer for measuring CO, as long as you are interested in ppm resolution over a 0-2,000 ppm range.  This frankly covers >90% of the applications.  Any analyzer in this range that uses an electrochemical sensor will not beat the Inspector's performance. If you are considering buying an expensive analyzer, compare the specs to the CO Inspector before you buy, and feel free to contact us with any questions.  We won't BS you, if the Inspector can't do the job you want to do, we'll tell you straight, but if it can, we'll tell you why and how.  

    8. I'm certain there's no CO around, why am I getting a ppm reading?

    Most likely there's an interfering gas/vapor present.The sensor used in the Carbon Monoxide Inspector was designed to be as selective as possible to CO, meaning it should respond to CO and nothing else. It's good, but not perfect.  The most common interfering gas is Hydrogen, with an ~10-15% cross sensitivity.  What that means is that if the CO inspector is exposed to, say, 100ppm of Hydrogen, it will display 10-15ppm.  The most common place we've found hydrogen is (and we say this with a straight face) human flatulence, which in some cases can be composed of several % hydrogen.  10,000ppm = 1%.  (So, 1% hydrogen would lead to a response of ~10,000ppm X 10%, or 1,000ppm, 2% hydrogen would likely cause the Inspector to display OL, for overload, as the max value is 1,999ppm). Other gases like methane will NOT cause the CO Inspector to respond.  Alcohols (like rubbing alcohol) should not cause the CO inspector to respond unless there is a significant amount near the gas sensor inlet.  So if you clean the face of the inspector with a little alcohol, it normally shouldn't respond unless you got carried away (e.g. directly hold a tissue soaked with alcohol over the sensor port). If you have any questions about the readings you are getting, feel free to contact Sensorcon and explain what you were doing.  We'll do our best to help you figure out what's happening.

    9. I'm confused, what's the difference between Carbon Dioxide (CO2) and Carbon Monoxide (CO)? (Carbon Dioxide (CO2) VS. Carbon Monoxide (CO))

    Carbon Dioxide (CO2) is NON-TOXIC, Carbon Monoxide (CO) is TOXIC...BIG difference! The CO Inspector measures Carbon Monoxide (CO), not Carbon Dioxide (CO2). If your chemistry is rusty, we understand. We hear a lot of customers (and many stores) mix up CO & CO2. The key difference is that CO only has 1 oxygen atom, and CO2 has 2 oxygen atoms. CO really wants to be CO2, so if it can't find a 2nd oxygen to cling to, it will try to cling to something else. If you breathe in CO, it will cling to the hemoglobin in your blood. Your hemoglobin normally likes to stick to oxygen too, but with CO around, it can't. This is why CO is toxic, it prevents your blood from clinging to oxygen (boy oxygen sure is popular!). CO2 on the other hand, is what we exhale. Both CO and CO2 can be formed by burning things: Whenever anything with carbon in it (e.g. paper or any hydrocarbon fuel) burns, it reacts the the oxygen from the air to form CO & CO2 (as well as other stuff). Ideally, only CO2 would be formed. In the real world, chemical reactions are never ideal, burning is no exception. If any part of the fuel is burned (reacted) with too little oxygen, it will form Carbon Monoxide (CO) rather than Carbon Dioxide (CO2). This is why the CO Inspector is useful for so many applications, anyplace there is a flame, there is a chance for CO to be present.  


    M1. Do I need to calibrate it, and if so, how?

    For the average Joe, it's not required for 2 years, but we have different recommendations for different applications.  A list of applications of increasing demand is below.

    Average Property Owner:  If you just want a rough idea of how much CO is present around the house or want to use the Inspector to find CO sources, and plan to leave it indoors, calibration is not normally required.  We recommend calibration or replacement after 2 years.

    General Purpose Professionals:  If you are a professional Home Inspector, HVAC Technician, Fire Department, EMT, or in a related field, we recommend calibration every 6-12 months to maintain the approximate +/-10% accuracy specified.  Exposure to fluctuating temperatures and humidity by leaving the device in a vehicle outside can cause the sensor output to change over time, with any inaccuracies increasing the longer it has been since the last calibration.

    Precision Professionals:  If you demand the highest accuracy, i.e. +/-10% or less, for applications like combustion analysis or medical applications, we recommend calibration every 3-6 months.

    Safety Applications:  If you are planning to use the CO Inspector for "mission critical" safety related applications, you are probably obligated to follow standards set by OSHA or another agency, which often call for bump or calibration testing every week or month.  In these cases you should follow whatever standards you are obligated to follow.

    How is calibration done:  You can send it in to Sensorcon for calibration for a $39 service fee, or do it yourself if you have calibration gas & a regulator with tubing (we recommend our supplier, Mesa Specialty Gases .  If you do it yourself, just hold down both buttons for 10 seconds to enter CAL mode, press the right button to zero (in known clean air) for 30 seconds, then apply the gas to the sensor port (you'll need 50ppm cal gas) for 1 minute, and you're done (the Inspector will automatically adjust itself accordingly).  

    M2. How long does the battery last?

    Years, unless it alarms a lot. The alarm condition consumes much more power than when the device is not in alarm (the flashing LEDs and buzzer use much more power than the sensor and LCD display).  Normally, the CO Inspector's battery should last 2-4 years. If the alarm is active a lot, it can drain the battery much sooner. If you ever need to replace the battery, it uses 1 standard CR123A Lithium battery (sometimes called a camera battery), which you can get from many retailers for $1-3 (click here to buy battery from amazon).

    M3. My past experience with gas detectors has included a lot of costly maintenance, how does the Inspector compare?

    The Inspector requires little to no maintenance. Average consumers won't have to do anything.  Professionals requiring high accuracy just need to perform occasional calibration.  We also have service plans that eliminate down time and maintenance for such professionals, contact us for more info.