Kidde is recalling almost half a million smoke detectors because a yellow cap left on during the manufacturing process can cover one of the two smoke sensors, making them unable to properly detect fires.

The company says it is recalling two types of dual-sensor model numbers with model numbers PI2010 and PI9010.

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.

​The company says there are about 452,000 of the smoke detectors in the U.S. and another 40,000 in Canada.

They were sold at various retailers and online between September 2016 through January 2018, and retailed for between $20 and $40.

To see if their units are defective, the company says consumers should visually inspect the smoke detector through the opening on the side of the alarm and see if a yellow cap is visible.

"If a yellow cap is present, the consumer should immediately contact Kidde to receive instructions and request a free replacement smoke alarm," the company said.