A coroner has urged homeowners to fit working smoke alarms after the deaths of a police detective and her two sons.
Heather Bickley, 46, and her sons Felix, 10 and Oscar, five, all died from smoke inhalation during a fire at their home on Anglesey in June.
An inquest at Llangefni heard that the fire probably started in a faulty freezer unit.
Coroner Dewi Pritchard Jones recorded accidental death verdicts and stressed the importance of smoke alarms.
The inquest heard the fire at the home of Mrs Bickley, who was a detective constable in child protection for North Wales Police, started slowly but spread to the ceiling of the home at Tyn-y-Gongl.
It then rapidly set alight the upper bedroom and roof space.
Neighbour Christopher Ryder said he was woken by the sound of the fire and windows breaking just before 01.00 BST on June 30.
"I started running until I got to the property," he told the inquest.
"The bedroom facing the right was completely ablaze. It was a complete inferno."
Mr Ryder ran back to his home and called the fire service, who arrived to find the whole property well alight, and no sign of the missing family.
By this time, Mrs Bickley's husband and father of the two children, John Bickley had arrived from working a late shift, to find his home on fire.
Richard Bryn Jones, watch manager for the North Wales Fire and Rescue Service described how his officers made a quick sweep of the downstairs of the property, but initially found nobody.
A little later, the fire officer spotted the body of Oscar through a window lying in the lounge of the house.
He told the inquest that officers with breathing apparatus dragged the boy from the house.
"I could see there wasn't a lot that we could do for the lad," he said.
The search for the other missing members of the family could not proceed, as parts of the house's roof began collapsing.
'Opportunity to get out'
The bodies of Mrs Bickley and her son Felix were discovered by a fire investigation team later in the day.
Mrs Bickley was found in the kitchen.
Fire investigation officer, Glyn Jones told the inquest that she may have been trying to investigate the cause of the smoke, when she was overcome by fumes herself and died.
The body of Felix was also found in the kitchen, but the inquest was told he had died in his bedroom from smoke, and his body had fallen to the ground floor when flames burnt through the ceiling.
Recording a verdict of accidental death on all three members of the Bickley family, the North West Wales coroner said they had all died from the effects of smoke inhalation.
He also said it was clear that there were no smoke detectors in the house.
He added: "When one looks at the fire and asks how can this be avoided, again the question of smoke detectors comes up.
"This isn't the first incident I have dealt with and it probably won't be the last.
"What can be learned is that smoke detectors save lives.
"Had there been working smoke detectors, Mrs Bickley and the children would have had a warning and would have had the opportunity to get out.
He said the deaths was especially tragic, because virtually an entire family had been wiped out in one incident.
"The presence of a detector could very well have saves all three," he added.