A carbon monoxide (CO) alarm is a time-weighted alarm. The way a time-weighted alarm works is by measuring the buildup of carbon monoxide in a house. For a person to begin feeling the effects of carbon monoxide poisoning, they would need to be exposed to a carbon monoxide level of 50 parts per million (PPM) for eight hours.

An alarm’s response time will vary depending on the level of carbon monoxide in the air. For example, an alarm will sound after three and a half hours of continuous exposure at a level of 50 PPM, but after only eight minutes of continuous exposure at a level of 400 PPM.

Levels of carbon monoxide exposure range from low to dangerous:
  • Low level: 50 PPM and less
  • Mid level: Between 51 PPM and 100 PPM
  • High level: Greater than 101 PPM if no one is experiencing symptoms
  • Dangerous level: Greater than 101 PPM if someone is experiencing symptoms

Carbon Monoxide Levels That Will Set Off Your Alarm

Carbon Monoxide Level   Alarm Response Time
40 PPM10 hours
50 PPM8 hours
70 PPM1 to 4 hours
150 PPM10 to 50 minutes
400 PPM4 to 15 minutes

Carbon Monoxide Levels and Their Symptoms

IMPORTANT: If your carbon monoxide alarm sounds, or you suspect you are experiencing symptoms of carbon monoxide poisoning, you should immediately leave your home and call 9-1-1.

50 PPMNone for healthy adults. According to the Occupational Safety & Health Administration (OSHA), this is the maximum allowable concentration for continuous exposure for healthy adults in any eight-hour period.
200 PPMSlight headache, fatigue, dizziness, and nausea after two to three hours.
400 PPMFrontal headaches with one to two hours. Life threatening after three hours.
800 PPMDizziness, nausea, and convulsions within 45 minutes. Unconsciousness within two hours. Death within two to three hours.
1,600 PPMHeadache, dizziness and nausea within 20 minutes. Death within one hour.

NOTE: For more information about your specific alarm, refer to your user’s manual.


A CO2 Monitor is a device that helps you record and understand the environmental Carbon Dioxide (CO2) levels in an office, room, building, factory, hospital or any other area. A CO2 Monitor can take once-off readings (with a handheld or portable reader), or automatically take readings over a period of time for you to review later (with a data logger, or CO2 logger).
It is important to monitor CO2 levels because they directly influence the mood, productivity and health of those exposed to CO2. Incorrect CO2 levels can cause stiffness, odours, drowsiness, and reduced productivity. Higher levels, or prolonged exposure, can be very harmful to health.

What Causes Indoor CO2 Levels to Rise?

The main cause of Carbon Dioxide indoors is people. The more people in an area, the more CO2 is emitted. Respiration of humans introduces this CO2. The amount emitted from one working person can be from 0.08m2 to 0.38m2 per hour, depending on the intensity of their work
 Gas operated devices such as heaters and kitchen appliances can also introduce CO2 into the area. It is also worth noting that CO2 is the main gas involved in the greenhouse effect, so higher levels of CO2 can be observed in areas with many windows (such as floor to ceiling windows in offices). The setup of the air conditioner and the proportion of indoor air to outdoor air being circulated will determine how this equates to the overall CO2 level in a room.
CO2 Levels are measured as PPM (Parts Per Million). The standard outdoor level is around 350ppm, and is the optimum level for freshness. However, you can generally get up to 600ppm indoor without any adverse effects. As you can see in this chart, once you get past 600ppm you will start noticing adverse effects.

CO2 levels have a noticeable impact on one's productivity and wellbeing. The higher the levels, the lower the productivity. The lower the levels, the better one can work. This is why it's important to measure and constantly conduct CO2 Monitoring within your workplace.



Almost every jurisdiction has standards and regulations which set out the maximum acceptable exposure to CO2 in workplaces and schools. Safe Work Australia's "Adopted National Exposure Standards for Atmospheric Contaminants in the Occupational Environment" outlines a Time Weighted Average of 5000ppm. This means average airborne concentration of Carbon Dioxide mustn't exceed 5000ppm.
There are other similar international standards which specify their own acceptable CO2 exposure limits:
  • The USA's Occupational Health & Safety Administration (OHSA) sets the limit at 5000ppm over an eight hour working day.
  • Schools in the United Kingdom mustn't be exposed to over an average level of CO2 over 1500ppm in a standard school day.
  • The Environmental Protection Administration in Taiwan sets a daily limit of 1000ppm in indoor areas, with a suggested level of 600ppm in areas such as schools, hospitals, and day care centres.
Please check with your local authorities for the latest standards which apply to you.
The natural concentration of carbon monoxide in air is around 0.2 parts per million (ppm), and that amount is not harmful to humans.
9 ppmCO Max prolonged exposure (ASHRAE standard)
35 ppmCO Max exposure for 8 hour work day (OSHA)
800 ppmCO Death within 2 to 3 hours
12,800 ppmCO Death within 1 to 3 minutes