Lifesaving battery-powered smoke alarms failed in more than a third of house fires in England last year, new analysis shows.
Firefighters attended more than 7,500 fires in homes with battery-powered alarms in 2018, but 38% failed to alert residents of the danger.
Incorrect positioning caused 45% of the failures, while missing or faulty batteries caused 20%.
The failure rate has barely changed since 2010, Home Office figures show.
The Local Government Association (LGA), which analysed the figures, has urged households to test their alarms in the run-up to Christmas.
Of 29,586 house fires attended in England between 1 April 2018 and 31 March 2019, 22,475 homes were fitted with a smoke alarm.
Battery-powered smoke alarms were found in 7,692 of the homes - but, of these, 2,899 (38%) failed to sound.
Mains-powered smoke alarms, by comparison, were less likely to fail, with failures reported in 21% of fires.
Industry figures suggest that one in 10 households do not have a working smoke alarm, while 22% never test theirs.
Last year, a property manager was jailed after after two young boys died in a fire in a rented house with no smoke alarms.
Three-year-old Logan Taylor and his brother Jake, two, died in the blaze in Fartown, Huddersfield in February 2016.
Kamal Bains, of Stableford Gardens, Huddersfield, whose property firm managed the house, admitted health and safety breaches.
During sentencing the judge told Bains: "Your failure to fit smoke alarms was a significant cause of the children's deaths."
The LGA has advised householders to fit more than one smoke detector in their homes, with at least one fitted on the ceiling of every floor.
Ian Stephens, chairman of the LGA's Fire Services Management Committee, said smoke alarms are "proven life-savers" and urged people to check theirs in the run-up to Christmas.
"With the increased potential fire risk from Christmas trees, decorations, candles and lighting, and people spending more time using heaters, open fires and cooking hot food during the colder winter months, anyone without a smoke alarm should buy and fit one as soon as possible," he said.
"They should also check the alarms of less able family members and those on their own - it may save their life."
How to maintain your smoke alarm
Test your smoke alarm when the clocks are changed
Vacuum it gently using the soft brush attachment to remove dust from the sensors
Change the battery at least once a year (unless it's a ten-year alarm)
Get a new alarm every 10 years
Source: UK Fire Service