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."