Smoke and Carbon Monoxide Detectors

Installing a smoke detector

In many countries, including Canada, having smoke and carbon monoxide detectors in the house is the law. The reason is simple: these alarms save lives. 

Danger of smoke 

Many house fires occur at night. If there is no smoke detector, those sleeping in the house may not notice the fire and will be overwhelmed by smoke in their beds. A working smoke detector can wake the family before it’s too late.  

Danger of carbon monoxide

Carbon monoxide is a colourless and odorless gas. It is produced by burning fuels such as gas, wood, oil, and coal. Most homes have an appliance that runs on one of these fuels. If the appliance is not vented properly or isn't working properly, the house can fill with carbon monoxide.

At first, carbon monoxide poisoning gives symptoms similar to those of the flu: fatigue, headaches, dizziness, nausea or vomiting, and shortness of breath. After a few minutes, carbon monoxide can cause you to black out, resulting in serious, permanent damage to the body. Eventually, carbon monoxide inhalation leads to death. A working carbon monoxide detector can alert you and your family to this danger. 

Choosing a detector

There are several different types of smoke and carbon monoxide detectors. Before buying one of these products, make sure your country’s safety stamp of approval is on the box. In Canada, it should read “ULC”, in the USA, the unit should have “UL” on the box. Smoke detectors and carbon monoxide detectors are sold separately, although there are duel detectors which serve both purposes.

There are two types of smoke detectors:

  • The ionization type smoke detector is better at detecting fast, flaming fires. These fires make up nearly three-quarters of home fires.
  • The photoelectric type smoke detector is better at detecting slow-burning smouldering fires that produce lots of smoke but little flame. 

Some smoke alarms use both types of detection. 

Currently, there is only one general type of carbon monoxide detector. 

Some alarms are battery-operated and some are plug in with a back-up battery.

Installing an alarm

Ideally, smoke and carbon monoxide detectors should be installed outside each bedroom and sleeping area, and on each level of your home, including the basement. They should be installed high on the wall and away from bathrooms, the kitchen, heating equipment, and ceiling fans. Read and follow the manufacturer's directions when you install your smoke detectors. 


Smoke and carbon monoxide detectors need some maintenance and will eventually need to be replaced. 

Test your alarm

Smoke and carbon monoxide detectors have a test button. You should push it once a month. If the unit does not signal an alarm, you will need to replace the battery and test again. 

Replace the battery

Replace the battery every six months. A good way to remember this is to put in a fresh battery when clocks are changed in March and November. If a warning beep is sounding, change the battery right away. 


Smoke and carbon monoxide detectors become less effective if they are clogged with dust. Follow the manufacturer's directions for cleaning your unit. 

Replace the alarm

Smoke alarms will not last indefinitely. A general rule is that the unit will have to be replaced every ten years. Write down the date you installed the alarm on the inside of the detector so you know when to replace it. If the alarm is no longer working, replace it right away

Around the house, sources of danger

It can be difficult to know if all your fossil fuel-burning appliances, such as the furnace, stove, and water heater, are working properly. These appliances should be professionally inspected at least once a year. Chimneys and vent pipes should also be regularly inspected and cleaned out to prevent carbon monoxide build-up and fires in general. 

During emergencies 

One of the most dangerous times for house fires and carbon monoxide poisoning is during power outages. When the heat and/or lights go out, sometime people use non-traditional methods to heat the house. They may burn things in a fireplace that has not been used or maintained in years. They may light camping stoves and lanterns or they may bring the barbeque inside to heat the house. Some may use a generator to provide power. These are all very dangerous things to do. Without proper ventilation, carbon monoxide can build up in the house. These items are also a major fire risk. 

When the detector's alarm sounds

Your family should develop an escape plan in case of fire or carbon monoxide buildup. Practice the plan and make sure the whole family, including children understand what to do if the alarm sounds. The escape plan should include an arranged meeting point outside the home.

More information

For more information, please read our pages on Burns: Household Safety and Prevention, Burns: Winter Safety, and Emergency Preparedness

Key points

  • Smoke and carbon monoxide detectors save lives.
  • Install a working smoke and carbon monoxide detector outside each bedroom and sleeping area and on each level of your home.
  • Test and clean your smoke detectors regularly and replace the batteries every six months.

Elly Berger, BA, MD, FRCPC, FAAP, MHPE

​H​ealth Canada