Yesterday while cooking I set off the smoke detector, no I did not burn anything. They go off when I cook over a high heat. And yesterday once they started going off they would not stop. I ended up having to disconnect them all (they are hard wired with an interconnect) and I replaced them this morning. Aaaaaaaand let me tell you, I had a sleepless night last night knowing there were no detectors installed.
https://www.southernliving.com/how-often-should-you-replace-smoke-detectors-8774122
In fact, smoke alarms with user-replaceable batteries became illegal in Scotland a couple of years ago.
Still waiting to see if the same regulation gets applied across the entire UK, but anecdotally I’ve noticed it’s already much harder to find anything other than 10-year battery or hardwired models in my part of England.
What’s the reason behind that legislation?
Safety. What else?
You can see a news report from when it came into force here: https://www.bbc.co.uk/news/uk-scotland-60203081
The guidance is here: https://www.gov.scot/publications/fire-and-smoke-alarms-in-scottish-homes/pages/where-and-what-to-buy/
Which includes this part on batteries: