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    Carbon Monoxide Inspector FAQ

    How accurate is the Inspector?

    Every Inspector is carefully 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.

    What is MAX Mode?

    MAX mode allows you to calculate the maximum amount of potential gas exposure at any given time. This can be useful you wanted to see the maximum carbon monoxide level that you are exposed to through a vehicles exhaust. Another instance where MAX mode would be useful is if you were to sample the exhaust from your chimney. Max mode is perfect for this because the concentration will change when the air mixes with it.

    In order to use MAX mode, simply press the MAX button. If an arrow is over the word MAX this is an indication that MAX mode is active.

    Why should I buy a pump?

    While the inspector does not require use of a pump, a pump can be helpful if trying to draw a sample from a hard-to-reach area.

    Sensorcon sells both a Carbon Monoxide and Hydrogen Sulfide Inspector kit. The kit includes the Inspector device, a carrying case, and a hand aspirated pump. The pump allows the user to quickly draw an air sample, in order to quickly assess the gas concentration throughout a larger area

    Should the Inspector be mounted on the wall?

    It is not recommended to mount the Inspector device on a wall, as the alarm is not as loud as traditional CO detectors. Ideally, the Inspector should be clipped onto your clothing or carried in your pocket for the most effective use.

    How does the Inspector differ from a CO detector from the hardware store?

    The inspector is a tool for measuring actual carbon monoxide concentrations above 35 ppm. A traditional hardware store CO detector is designed solely to sound an alarm when concentrations are elevated for extended periods of time.

    CO Concentration Ul2034 CO Detectors Sensorcon CO Inspector


    Nothing happens from 0-30ppm.

    Instant readout on LCD display in 1ppm increments.


    Probably nothing At 30ppm+. Though there is a small chance that it will alarm but not for at least 30 days! Please consult the UL2034 standard which states that the device is not supposed to alarm for at least 30 days 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 first alarm starts instantly at 35ppm+. This corresponds to the 8 hour time weighted average (TWA) set by the National Institute for Occupational Safety and Health (NIOSH)


    At 70+ppm the alarm is supposed to start in 60-240 minutes.

    Instant numerical readout and
    alarms active.


    At 150+ppm the alarm is supposed to start in 10-50 minutes.

    Instant numerical readout, alarms active, higher alarm starts at 200ppm, which corresponds to the 15 minute ceiling set by NIOSH. Ceiling means this is the maximum workers should be exposed to for any period of time.


    At 400+ppm the alarm is supposed to start in 4-15 minutes.

    Instant numerical readout = high alarms active

    I’m getting a ppm reading. What does it mean? What should I do?

    Concentrations less than 5 ppm shouldn’t be too concerning. Although, it may be wise to keep an eye on it.

    ppm Reading Possible Meaning What you should do

    0-5 ppm

    CO is normally present in the air at Electronics Noise (Our sensor is accurate to 2ppm)

    Monitor it. Its normal to see small transients of 1-2ppm. If it stays in the 3-5ppm range then there may be a very small amount of CO present.

    Concentrations moving between O & 2 to 3ppm are typically sensor noise. This happens when the instrument is adjusting to a new ambient temperature.

    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 with improper venting.

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

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

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

    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 around you or you may be close to a burning fire.

    These concentrations are higher than you should be exposed to over extended periods of time. Unless you are performing an exhaust test. If you can smell exhaust then you are not smelling CO (CO is odorless). You are smelling other gases such as NOx. However, 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.

    35 ppm+

    Indoors: These concentrations are considered hazardous and are almost certainly coming from a large leak in
    a furnace or boiler.

    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. This 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 then you should not stay in this environment for very long until the CO source is found and corrected.

    How does the Inspector compare to other portable Carbon Monoxide detectors?

    The Inspector combines a rugged, compact, quality design with excellent ease of use at a low cost. There are three kinds of portable carbon monoxide detectors sold on the market today:

    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 and most have a MAX mode, require occasional calibration, and typically cost $200 to $400. Support for these products is virtually nonexistent and since the companies that sell them generally don't manufacture them. Sensorcon's carbon monoxide Inspector is made to the highest quality in the USA. It is rugged, water-resistant, has a standard battery that lasts for years and is fully supported by our knowledgeable staff.

    Safety Carbon Monoxide Detectors: These are compact devices sold mainly by large gas detector companies for around $100 to $400. These companies are concerned with selling high volumes to large mining or industrial operations and they require frequent calibration. Sensorcon's carbon monoxide Inspector is just as small and robust as these safety oriented CO detectors. However, it is much easier to use. Sensorcon's support staff will answer any questions or concerns. We're not just making products for large companies. If you're a one man shop or just an average consumer that wants better information about carbon monoxide, we're here for you too.

    Carbon Monoxide Analyzer: If you see the word "analyzer" it usually only means you will pay more. This being for the same technology and only a more fancy looking device. Maintenance issues are much higher. You can use our carbon monoxide Inspector for almost any application that you can use an analyzer for in measuring CO. As long as you are interested in ppm resolution over a 0-2,000 ppm range.

    This frankly covers about 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 then please compare the specs to our carbon monoxide Inspector before you make your purchase.,
    Feel free to contact us with any questions.

    I am certain there is no Carbon Monoxide around. Why am I getting a ppm reading?

    It is quite possible that there is an interfering gas or vapor present.

    The most likely interfering gas is Hydrogen with a 10-15% cross sensitivity. This means that if the Inspector is exposed to 100ppm of Hydrogen it will display a reading of 10-15ppm.

    Other gases like methane will not cause the Carbon Monoxide Inspector to respond. Alcohols also should not cause the Inspector to respond, unless there is a significant amount near the gas sensor inlet. Cleaning the face of the Inspector with a small amount of alcohol should not cause the Inspector to respond.

    If you have any questions about the readings you are getting, please feel free to contact Sensorcon. We will do our best to help you figure out what is happening.

    What is the difference between Carbon Dioxide (CO2) and Carbon Monoxide (CO)?

    Carbon Dioxide (CO2) is NON-TOXIC, Carbon Monoxide (CO) is TOXIC. CO really wants to be CO2. If it can't find a 2nd oxygen to cling to, then it will try to cling to something else. If you breathe in carbon monoxide it will cling to the hemoglobin in your blood. Your hemoglobin normally likes to stick to oxygen too but can't with carbon monoxide around.

    Therefore, carbon monoxide is toxic and it prevents your blood from clinging to oxygen. 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 burns, it reacts to the oxygen from the air to form CO & CO2. 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 with too little Oxygen, then it will form Carbon Monoxide (CO) rather than Carbon Dioxide (CO2). This is why the carbon monoxide Inspector is useful for so many applications including anywhere there is a flame and a chance for CO to be present.  

    Device Maintenance FAQ

    Do I need to calibrate the device? How is this done?

    When shipped, our meters are calibrated and tested to read within +/-10% of the calibration gas applied. Over time, all electrochemical sensors will drift, and we estimate our sensors to drift ~10% every 6 months. For the best accuracy, we recommend calibrating the sensor every 6 months. With this in mind, the user may choose to adopt a different calibration schedule.

    The Average Property Owner: If you just want a rough idea of how much carbon monoxide is present around the house or you want to use the Inspector to find other CO sources, then the home owner may decide to not calibrate the sensor every six months. However, after two years, the sensor will read end of life (eol) and we recommend the homeowner send the sensor in for calibration.

    General Purpose Professionals:  If you are a professional Home Inspector, HVAC Technician, Fire Department, EMT, or in a related field, then we recommend calibration every 6 months to maintain the +/-10% accuracy specified. Please note that exposure to fluctuating temperatures and humidity can cause the sensor output to drift over time; therefore, we don't recommend storing the sensor in a vehicle or leaving the device outside when not in use.

    Precision Professionals:  If you demand the highest accuracy, (+/-10% or less) for applications like combustion analysis, energy audits, or medical applications then we recommend a calibration every 3 to 6 months.

    Safety Applications: If you are planning to use the carbon monoxide Inspector for "mission critical" safety related applications, then you are obligated to follow standards set by OSHA or another agency. This will often require daily bump testing and monthly calibration.

    How Is Calibration Done: You can send it in to Sensorcon for calibration or do it yourself if you have calibration gas & a regulator with tubing. We offer calibration gas accessories on our web store.

    If you'd prefer to do it yourself then simply hold down both buttons for 5 seconds to enter CAL mode. Then press the right button for 30 seconds to set a new zero; make sure you are in an area where no carbon monoxide is present. Finally, apply the 50 PPM calibration gas to the sensor port for 1 minute. The sensor is now calibrated. If you want to verify the calibration was done correctly, wait until the sensor reading has gone back to zero. Then reapply the 50 PPM calibration gas. The reading should be within +/- 10% of 50 PPM.

    How long does the battery last?

    Typically, the battery should last between 2-4 years. However, if the alarm is active on a regular basis, the battery can drain much quicker. The battery can be replaced with one standard CR123A Lithium battery.

    How much maintenance does the Inspector require?

    There is very little maintenance required for Inspector owners. The average consumer won’t have to do any maintenance. Professionals requiring a high degree of accuracy will simply need to perform occasional calibration. We also have service plans that eliminate down time and maintenance for such professionals.

    If you have any further questions, please do not hesitate to contact us for more information.


    Phone: 1-716-276-2976  
    E-Mail: sales@sensorcon.com  

    Hours of Operation:
    Monday through Friday
    8am to 4pm