A Christchurch couple are thanking their smoke alarms for saving their lives after fire tore through their home.

Marie Musson and partner Derek Petch were only alerted to the blaze once their alarms went off.

"We had no idea fire had taken hold of the property until the smoke alarms went off," Musson said.

The smoke alarms were not only working but had also been recently upgraded, she said.

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"Thankfully, we were able to get out safely, but without the warning, it could have been very different. I can't emphasise enough the importance of up-to-date smoke alarms."

The blaze started in a neighbouring Alvaston Dr duplex and spread through the roof and took four minutes to destroy both properties.

Andrew McCarroll, of Smoke Alarm Professionals, is Marie's grandson and recently upgraded the properties smoke alarms.

"I know smoke alarms save lives, but I never thought they would save the lives of my family.

"They'll need to rebuild and replace photos and mementos destroyed in the blaze, but they're alive and uninjured, and that's the most important thing."

Smoke Alarm Professionals chief executive Cameron Davis said Fire and Emergency New Zealand figures showed only 87 per cent of New Zealand homes had working smoke alarms.

"Working smoke alarms should be in every home, but 13 per cent of New Zealand residents are gambling with their safety and the lives of family and friends.

"Nobody thinks it'll happen to them, but home fires will claim the life of at least one person this month.

"The best investment families, landlords and property managers can make this summer is up-to-date, working smoke alarms."