The Best Guide to Oxygen Detectors (Expert Explains)

Oxygen Analyzer, Oxygen Detector, Oxygen Monitor -

The Best Guide to Oxygen Detectors (Expert Explains)

Oxygen detectors are one of the most essential gas detectors due to the importance of oxygen to human life. Oxygen detectors are an important safety device to alarm when oxygen levels have reduced, to help avoid occupational dangers. An oxygen detector is a small handheld unit that instantaneously detects the oxygen levels and displays it on the digital display. In the recent years, the price of oxygen detectors has reduced and can be purchased for less than $200.



  • O2 analyzers can be as low as $200.
  • Oxygen sensors last from 2 to 3 years.
  • Oxygen is the gas of life and is abundant in air at 20.9%. Detecting and alarming low oxygen levels is important for health and occupational safety.
  • Oxygen can be displaced and becomes dangerous to life when less than 19.5%.
  • Oxygen can become dangerous at enriched levels and low level - so precaution is needed.
  • Highly accurate and specialized oxygen sensors can be expensive.

Why is Oxygen (O2) gas so important?

Oxygen helps sustain life on earth. Without oxygen our planet would be lifeless. Humans and animals need oxygen to survive. When oxygen levels decrease, a dangerous situation can occur - such as oxygen deficiency which leads to human asphyxiation. An oxygen detector is important to alarm humans when oxygen levels decrease.

O2 is the chemical formula for oxygen. There is 20.9% of oxygen in the air. Detecting oxygen levels is very important in our modern lives. Some examples include:

  • Detecting oxygen in manufacturing processes. Sometimes enriched or depleted oxygen in required.
  • Detecting oxygen in life support systems such as those used in spacecrafts, aircrafts, submarines, and vet hospitals. 
  • Detecting oxygen in gas bottles used in scuba diving.
  • Detecting oxygen to help support human and animal health.
  • Detecting oxygen to confirm that little or no oxygen exists, such as in welding situation, modified atmosphere packaging situations or nitrogen flush purging processes.
  • O2 is used in welding torches

What does an Oxygen Detector do?

Oxygen detectors measure the amount of oxygen in air shows as a % value. An oxygen detector is a handheld unit with alarm functions to warn when oxygen reaches preset levels that may be dangerous.  

Oxygen detectors are sometimes called oxygen meters, oxygen monitors, or oxygen analyzers. They all refer to an oxygen measuring instrument that has the ability to alarm and also measure the oxygen concentration in %vol or parts per million (ppm).

How does an Oxygen Detector Work?

An oxygen detector works by using an electronic sensor to detect oxygen concentrations. The most common sensor used for oxygen detectors, is an  electrochemical sensor cell.

An oxygen detector is made up of two main parts:

  • The electronics that has a microprocessors with with analog to digital converters. 
  • The electrochemical oxygen sensor which is a galvanic cell. It outputs electrical energy from the electron transfer in a redox reaction modulated by the oxygen being detected. The oxygen sensor is a partial pressure sensor that outputs a voltage proportional to the oxygen concentration. 

When the oxygen detector is "calibrated", it is able to detect oxygen from 0 to 30% (as an example).  A linear extrapolation take place from the from zero point calibration (usually pure nitrogen) to 20.9% (air oxygen concentration). 

How does an Oxygen Sensor Work?

The most common electrochemical oxygen sensor is the Alpha Sensor (see below). Its profile, dimensions and working principle is very similar to many others electrochemical sensor cells.

The sensor works when oxygen gas molecules permeate into the sensor and react with a working electrode triggering an electrochemical redox reaction. Current is generated proportional to the oxygen level detected.

oxygen sensor alpha

What are the different types of Oxygen Detectors?



Oxygen Detector for Personal Protection


The majority of Oxygen detectors are portable types. These are small battery-powered units with a oxygen sensor that can be clipped to enable continuous personal protection.

oxygen waterproof detector
Oxygen Detector with pump for Point Sampling

This is a oxygen detector with a built-in pump or an external pump. Sometimes the oxygen detectors with built in pump are called oxygen analyzers. A probe is used to enable point sampling. These are used to analyze oxygen content for food packaging, welding applications and nitrogen purging in industry.

o2 analyzer

Oxygen Detector Oxygen Monitor for Stationary Fixed Wall 

Fixed wall-mounted units provide continuous protection. These units are more expensive and offer protection, in an industrial facility or confined space.

fixed wall mount H2S monitor


What is the difference between different oxygen sensors?

O2 Sensor Technology

Working Principle




Ultrasonic Sensors

The speed of sound is a function of the molecular composition of the gas. Detecting the speed and attenuation is proportional to the oxygen content.
  • Easy to integrate with electronics
  • Immediate ON
  • Long Life
  • Long calibration stability
  • Medium Expensive
  • More bulky than electrochemical cells



The oxygen gas reacts with a working electrode triggering an electrochemical redox reaction. A current is generated that is proportional to the detected oxygen levels.
  • Small & Cheap
  • Easy to integrate with electronics
  • Immediate ON
  • Limited life from 24 to 36 months
  • Influenced by temperature and humidity



The zirconia allows  oxygen ions to travel so when exposed to gases at different concentrations an electrochemical voltage is generated.
  • Very accurate
  • Large Detection Range
  • Requires control hardware
  • Very Expensive
  • Requires heating and power

What is Oxygen Deficiency?

Oxygen deficiency is life-threatening and cannot be detected by our sense of smell. As a general rule, oxygen deficiency is caused by the release of inert gases, which then in turn displace oxygen.

Since roughly one-fifth of the atmosphere is oxygen, the oxygen concentration is only reduced by one-fifth of the concentration of inert gas. For example, if 10% of helium is released into the atmosphere, the oxygen concentration decreases by 2%, while the nitrogen concentration is reduced by 8%. Because liquid nitrogen (-196 °C) is often used in industrial areas, a dangerous oxygen deficiency can quickly arise due to the evaporation of this liquid nitrogen.

What are Safe Oxygen Levels?

When oxygen is deficient, which means when the oxygen level decreases, it becomes dangerous to humans and animals (typically less than 19.5%). Humans basically suffocate, which is termed asphyxiation. This can be a big problem in occupational environment such as confined spaces like silos, tanks, manholes, tunnels and chambers.

When humans breath low oxygen mentions the following symptoms of hypoxia can include:

Various government agencies and associations have recommended oxygen gas limits. Some examples are in the below table.


Recommendation / Requirement

Occupational Safety and Health (OSHA)

Air is considered oxygen-deficient below 19.5%

National Institute for Occupational Safety and Health (NIOSH)

Air is considered oxygen-deficient below 19.5%

American Conference of Governmental Industrial Hygienists (ACGIH)
<18% is minimum partial pressure without need for respiratory protection at normal atmospheric pressure

Are high levels of Oxygen dangerous?

A increase in oxygen may be problematic as too much may lead to hyperoxia causing oxygen toxicity or oxygen poisoning that may damage the lungs, damage cell tissue and may induce coughing and trouble breathing. 

An oxygen detector typically has two alarms. A low alarm that triggers when oxygen levels decrease and reduce past a set-point. They also have a high alarm. This is to alarm when enhanced oxygen or concentrated oxygen exists.

What is an Oxygen Detector used for?

There is a plethora of applications that call for the use of an oxygen detector. A generic list that captures some of them is highlighted below.

  • Veterinary: Oxygen therapy is administered to animals under various situations. Hence the requirement for an oxygen analyzer to ensure the correct amount of concentration is being provided to the animal.
  • Food Packaging Analysis: Used in many food industries as a quality control check to ensure modified atmosphere packaging equipment is operating correctly. Typical requirements includes O2 measurement range from 0 to 100%, with 0.01% resolution and built-in pump. 
  • Nitrogen Flush and Leakage Testing: Many industrial systems and equipment incorporate nitrogen gas supply and monitoring of leaks is essential. This is done by detecting residual oxygen. Typical requirements includes O2 measurement range from 0 to 100%, with 0.01% resolution and built-in pump.
  • Scuba Tank Oxygen Supply: Scuba divers use air cylinders and enhance oxygen air supply when diving. Before using the cylinders, they often use oxygen analyzers to confirm and validate the oxygen concentration. Typical requirements includes O2 analyzers to detect enhanced oxygen ranging from 21 to 100%.
  • Flue and Exhaust Gas: A combustion process burns fuel with oxygen. It is often that oxygen is measured to help tune and optimize the air-to-fuel ratio. This occurs in automobiles, gas powered appliances and more sophisticated combustion processes such as power generation. Typical oxygen ranges required is 20.9 to 0% with 0.1% resolution. 

How can I Test my Oxygen Analyzer?

The best way to test your oxygen detector is to expose it to nitrogen. Since air has 20.9%, perturbing this concentration and bump testing it to pure nitrogen or reduced levels is a valid check. If you analyzer or meter has alarms, verify they are operational.  Spray the gas onto the sensor to confirm sensor and LED and buzzer alarm operation. 

Will my Oxygen Detector alarm if I breath on it?

If you breath onto your O2 detector, it will quickly decrease in O2 reading as breath exhalation has depleted oxygen levels, about 17%. The below video analyzes oxygen exhalation.

    What is the Best Oxygen Analyzer brand?

    There are many oxygen analyzers on the market. The reputable brands used to detect elevated oxygen coming from oxygen sources and concentrators includes the following:

    How do I select an Oxygen Detector?

    To select the best oxygen detector that serves your purpose follow this guide. To narrow down your selection answer these questions:

      • What oxygen detection range do I need?
      • What resolution do I need?
      • How often will I use it?
      • What is my budget and operating cost budget?
      • Does my application require any special product requirement such as pump, such as accreditations, waterproof ability?
      • Do I need advanced functions such as battery operation? Detection of flow or pressure?
      • Do I need it to be a stationary fixed wall unit?

    Based on these answers you can quickly narrow down a product for your purpose. You may need to compromise of features to adjust for your budget.

    What are specialized oxygen detectors?

    Some niche application have unique requirements when it comes to oxygen detection. These applications have garnered unique oxygen measurements and function specifications. Each application calls for special oxygen detector functions and attributes. Examples include the following:

      How long do Oxygen Detectors last for?

      An oxygen detectors that employs electrochemical sensors will last between 24 to 36 months. 

      Can an Oxygen Gas Detector measure dissolved Oxygen?

      No, it cannot. To measure dissolved oxygen, a specific oxygen meter for water must be purchased. An oxygen gas detector only measures oxygen in air. A different detector that uses different technology is required to measure oxygen in water, which is more commonly referred to as dissolved oxygen.

      Is it better to detect Oxygen or Carbon Dioxide for indoor air quality?

      It is better to measure carbon dioxide. A CO2 monitor will detect carbon dioxide levels with 1 ppm resolution. A oxygen detector will be measuring, at best, 0.1% resolution (which is 1000ppm). So it is clear, that CO2 will allow for more sensitivity and high measurement fidelity. So all things being equal (including price), your better option is to measure CO2 for basic home indoor air quality measurements.

      But, if the space is a "confined space", then using an oxygen detector to alarm when oxygen is depleted is recommended. 

      Is it worth replacing my Oxygen Sensor in my Oxygen Detector?

      Some manufacturers offer oxygen replacement sensors and some do not. The gas sensor replacement business is a very lucrative business model. The cost effectiveness strongly depends on the price of a new unit. 

      In most instances, the cost of replacing a sensor out-weighs the cost of purchasing a new gas detector unit. Consider the cost analysis below under these two scenarios.

      Scenario A: Purchasing a New Oxygen Detector

      Model FD-90A-O2. Portable Oxygen Detector. Retail Price: $145

      Scenario B: Cost of a Oxygen Sensor Replacement

      New O2 Sensor = $83.90

      Engineer Time to Replace = 15 min @ $100/hr = $25

      Calibration to NIST Traceable Pure Nitrogen = 15minutes @ $100/hr = $25

      Administration overhead = 10minutes @ $60/hr = $10

      Total = $140

      Analysis = $145 (new detector) versus $140 (replacement sensor). Which option will you choose?

      What is Oxygen Detector Bump Testing?

      • Bump testing is a procedure when one exposes the gas detector to a small amount of “blast” target gas to ensure the detector operates as expected. 
      • Since the target gas "oxygen" exists in the atmosphere, bump testing oxygen detectors is typically undertaken using pure Nitrogen gas. 
      • The function of this test is to verify detection operation and build user confidence, particularly in hazardous and critical user applications.
      • It is recommended to bump test when first purchased. Weekly thereafter especially in LIFE THREATENING and or DANGEROUS applications in order to verify detector operation. See video explanation here

      How do I take care of my Oxygen Detector?

      • Store your oxygen detector at normal room temperature - about 70F with 50%RH (well within operating specifications).
      • Store it away from electromagnetic or magnetic sources such as phones.
      • Store it in a clean environment where no dust or particles exist.
      • Store it away from any exhaust gas, concentrated vapors, harsh chemicals that may poison the sensor.
      • Clean the casing of your detector with a damp cloth.
      • Store it in a stable place where there are no vibrations or continuous shaking.

      How do I properly use an Oxygen Detector?

      When operating an oxygen detector, there are some tips to consider. Obviously, be smart and read your product manual. But do keep these tips in mind:

      • Ensure the oxygen detector has been bump tested and validated operational. Check to make sure it is reading 20.9% in fresh air. If it is 20.8% or 21.0%, that is OK. If it is fluctuating beyond that, give it a quick calibration to fresh air so it displays 20.9%.
      • When using a personal protection oxygen detector, turn it ON, and keep it on your man. Set your alarms as desired.
      • If undertaking analytical measurements, keep the unit stationary. Ensure humidity and temperature is also tracked and are as constant as possible.
      • Recovery time (i.e. time to come back to 20.9%) is typically longer than the response time of the oxygen sensor.

      What is the difference between a ppm and % Oxygen?

      The typical scale of concentration for O2 is ppm or %.

      In most cases, Oxygen % unit is used much more often since 20.9% concentration is in the air. The parts per million scale (ppm) is used when low levels of oxygen may be present - which is easier to communicate in the ppm scale than the % scale. For example, easier to communicate 10ppm rather than saying 0.001%. 

      Conversion Example

      O2 % value = (O2 ppm / 1,000,000) x 100%

      For example, if we have 5,000 ppm of O2, then we obtain

      O2 % value = 5,000 / 1,000,000) x 100%

      O2% value = 0.5%

      Quick Conversion

      10ppm = 0.001%

      100ppm = 0.01%

      1,000ppm = 0.1%

      10,000ppm =1%

      100,000ppm =10%

      1,000,000ppm =100%

      Final Words

      Oxygen detectors are one of the most essential gas detectors due to the importance of oxygen to human life. Oxygen detectors are an important safety device to alarm when oxygen levels have reduced, to help avoid occupational dangers. An oxygen detector is a small handheld unit that instantaneously detects the oxygen levels and displays it on the digital display. In the recent years, the price of oxygen detectors has reduced and can be purchased for less than $200.

      About The Author

      Dr. Koz is the Chief Engineer of Forensics Detectors. The company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing, and testing toxic gas detection systems for over 20 years.

      gas detector expert

      Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and having a cold beer. 

      Read more about Forensics Detectors here.

      Phone: +1 424-341-3886

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