Safety concerns for British Standard-approved fire alarms have been raised after tests revealed large variations in the time they take to sound, with one failing to go off at all.
The Which? investigation found that smoke alarms can have "wildly varying" response times while still having met the standard and received the Kitemark certification.
What did the tests involve?
The investigation consisted of four controlled fire tests involving smouldering wood, solvent, plastic and cotton fires on 15 different smoke alarms.
In two of the tests, the Devolo Home Control Smoke Detector failed to sound at all.
Across all four types of tests, there was a pattern of largely varying response times.
In the smouldering wood test, the First alert SA300Q and the EI Electronics Ei3500S took more than nine minutes to trigger, while the Nest Protect Smoke and Carbon Monoxide Alarm were over four minutes quicker to sound.
In response to the results, Which? has raised concerns on the danger of slow reacting fire alarms and has called for a new, tougher standard that only rewards models that have a quicker response time.
Alex Neill, Which? managing director of home products and services, said: "People will be surprised to see such a big variation in response times from alarms that are currently classed as being safe and which pass the standard.
"We want to see stricter testing criteria because every minute counts in a fire."
Devolo have responded to the tests, saying the detector in question passed test procedures in two certified German laboratories and all its alarms were certified in accordance with EN 14604.
The German manufacturer said: "These results are a matter of serious concern for Devolo. Safety is the company's number one priority and we meet the highest international standards.
"We are therefore extensively investigating all details of the test in co-operation with our partners."
The British Standards Institution said: "The test fires set out in the standard are designed to ensure that whichever technology is used or the type of fire encountered the smoke alarm provides adequate warning in the event of a real fire.
"The test fires are not designed to ensure all detectors respond similarly.
"Smoke alarms are allowed to respond earlier than the limits and often do."