Briilea gas detector?

Does the manual suggest anything?

Contact support(at)briidea.com

Point out there is no user manual available on their website. Ask them what to do to solve the fault.
I suspect it'll be to replace the whole unit, especially as it seems to be a generic Chinese item, based on the awful wording on the products web page.
"The service life is 5 years. After 5 years, it will be sent out to remind you that the product is expired to escort your safety".
If they suggest replacing the sensor be sure to ask how to recalibrate the unit.
Personally, I would replace the whole thing, given that it is safety critical.

Rbrhr
August 2022