Health Canada is recalling 40,000 smoke alarms due to a defect that could prevent them from detecting fires. And the London Fire Department is urging people to take action if they have the defective units.

The alarms are produced by Kidde and contain the model numbers PI2010CA and PI9010ca.

The word "Kidde" is printed on the front centre of the smoke alarm. The model number and date code are printed on the back of the alarm.

Is your alarm is defective?

According to the fire department, they contain a yellow cap inside that can block the two internal sensors. This can compromise the alarm and fail to alert homeowners to a fire.

The company's recall notice instructs people to take the alarm down from the ceiling and turn it on its side. If it has it has the yellow cap -- which can be seen through openings on the side -- it is one of the affected models and must be replaced.

Kidde then advises that the alarm be reinstalled until a replacement can be obtained.

Chief concerned

Consumers with the faulty units are urged to make an immediate request through the company's website for a new device.

"I'm concerned that many people may not hear about the recall and, if they do, they may not reinstall the alarm they take down," said Acting Deputy Fire Chief Jack Burt in a news release issued by the London Fire Department on Friday.

Anyone who needs clarification about the details of the recall is urged to call the fire department at 519-661-4565.

In addition to the 40,000 defective alarms in Canada, another 452,000 are being recalled in the United States.