Research report

Why do long-life smoke alarms fail early?

We tested samples of 10 different long-life alarms and came up with a theory.

By Paul Smith

Former Head of Test | Kaiwhakahaere Whakamātautau

Anyone who’s been through the annual pain of taking smoke alarms down from the ceiling to change the battery knows fit-and-forget is worth paying for.

Why is this free?

This report is free thanks to funding from MBIE Tenancy Services.

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However, our recent member survey shows one in five smoke alarms claiming a 10-year battery life isn’t going the distance – they failed within five years.

That’s twice the failure rate of models with replaceable batteries. “Early failure of long-life batteries” is to blame in half of dead 10-year alarms.

Stats for alarms bought in the past five years

10% of replaceable battery alarms failed (276 responses).
20% of 10-year battery models failed (501 responses).
“Too many false alarms or chirps” was a common reason for failure in both types of battery-powered alarms (70% of replaceable model failures, 65% of long-life model failures).
Why are more 10-year battery models failing? “Early failure of long-life batteries” was reported in 47% of failures.

What our test found

We bought samples of 10 different long-life alarms and tested them in our lab. We measured battery capacity, how much juice was used while they silently watched for smoke, how much was used when the alarm sounded and how much capacity the battery would lose over 10 years.

Our testing found long-life alarms should be able to go the 10-year distance; they simply shouldn’t be failing at the rate our members reported.

Why are so many alarms failing?

The difference between our survey and testing has us baffled. But we have a theory: it could be down to the condensation that forms in damp, uninsulated homes.

After having the heating cranked up to make our homes bearable on cold winter nights, once we go to bed and the temperature drops, condensation starts forming (that’s the crying windows many of us see each morning). Could this condensation affect your smoke alarm? Our theory is that dampness in the circuits means the “standby” mode uses much more juice than intended, shortening battery life.

We put our theory to the test in the same temperature- and humidity-controlled room we use to test heaters and dehumidifiers. Unfortunately, while we noticed a slight difference in power use when the dampness increased and observed a couple of models become more prone to sounding a false alarm, our testing showed nothing conclusive.

How do you demand a fix? Keep a record

How long should a product last? It’s not a clear-cut answer – the Consumer Guarantees Act leaves it open for consumers, retailers and manufacturers to debate. But when a product proudly claims a “10-year battery life”, it isn’t up for discussion.

“We couldn't find the receipt from the store we bought them from and they didn't want to know about them without the receipt.”

Does that sound familiar? A somewhat long-serving device (such as a smoke alarm or LED bulb) bites the dust before its time but you’re stumped on how to claim a replacement for it. When did I buy it? Where’s the receipt? How much did it cost?

There’s an easy solution. Take a digital photo of the receipt (or scan it) and store it away (in the cloud or on a device). A digital receipt is proof of purchase – enough to go back to the retailer and demand a fix.

When a product proudly claims a “10-year battery life”, it has to live up to that claim.