The blaze then activated the automatic sprinklers in the bedroom and hallway, dousing the fire and ensuring it couldn't spread.
The woman was taken to Whangārei Hospital as a precaution but discharged later that morning.
The bed, wall and ceiling in the affected room were fire damaged, and about half the house had water damage.
The incident showed the value of smoke detectors and automatic sprinklers, Bain said.
''Early warning from the smoke detector saved lives, and the sprinklers saved the house.''
Two appliances from Whangārei Fire Brigade responded.
Bain said the fire had started on the bed and may have been caused by an appliance. He was still working to pinpoint the precise cause.
It was not caused by a cigarette and no one at the home at the time was a smoker.