A Manitoba couple says they narrowly avoided dying in their sleep last week when poison gas leached up into the master bedroom of their two-storey home in the middle of the night.

"Everything was kind of a fog until we actually stood up and realized this has to be dealt with, we can't just roll over," said Dave Williams, 57, who lives 50 kilometres southeast of Winnipeg in Steinbach.

He and his wife, Claudette Williams, 55, were fast asleep early Friday morning when they awoke to the sound of a  "faint alarm" on the first floor of their home.

They were confused and disoriented, Dave Williams said, as carbon monoxide was leaking and had already begun to affect them.

"I guess the adrenaline kicks in and you have to move, but your first response is 'Shut that alarm off, leave me alone,'" Williams said. "Then all of a sudden something inside of you goes, 'No, this is real.'"

They have an alarm system that a company monitors remotely. Williams said on top of the initial alarm, the voice of a worker at the company was eventually projected through an intercom in the home to alert the couple about the leak.

Then Williams' cellphone rang — a second failsafe from the monitoring company meant to ensure homeowners are aware of a leak.

"They said, 'Get out of your house,'" he said. "It's all a bit of a blur exactly how that all happened, because we were a little bit dopey already."

The pair opened all the doors of their home before they went outside and called 911.

'That one failed us'

The couple has three carbon monoxide detectors in the home. One in the basement sounded during the leak but was out of earshot and the couple didn't hear it until they were already out of bed.

A guest was staying in a room in the couple's basement at the time and was woken by that alarm. Williams said there was very little carbon monoxide in the basement and the man was "quite fine," apart from being confused.

A second alarm on the main floor sounded, and that's what the couple heard. But Williams said a third alarm on the main floor, closest to their bedroom, did not go off.

"The digital read out on it read 54 parts per million [carbon monoxide], but it never rang," he said.

"It had a little yellow light on it that says, 'Fault.' So was that faulty before or did it become faulty? That one failed us, and that was actually not very old, less than a year."

An inspector arrived with emergency crews and tests showed levels of the odourless, poisonous gas were still very dangerous, Williams said.

"The levels in our master bedroom were still extremely high," Williams said, adding the inspector told them if their grandchildren had been spending the night, they might not have survived.

"That's scary.… That was very sobering. We have several grandchildren and they are often at our house."

Williams said he and his wife are feeling much better now.

He credits one of the first floor carbon monoxide detectors for saving their lives, but advises everyone to install a detector close to their bedroom.

"My understanding was that carbon monoxide was a basement problem," Williams said. "That is false, I've learned."

It's still unclear what caused the leak, but Williams said it could be a section of chimney inside the wall rather than the home furnace.

More from CBC Manitoba:

With files from Janice Grant and Information Radio