Question about Netatmo NSA-EC-2

Yes, but it has lasted with me for years. Glg

Smoke detectors must be replaced after approx. 10 years. It may happen that the sensor no longer works properly.

You do not HAVE to replace them. There are 2x CR17450E-R FDK 3v 2400mAh lithium built-in.
With a little skill you can get them replaced, but I think the batteries will most likely outlast the life of the product.
I would ask myself whether Netatmo is the right product. It took me a few attempts to get the setup working (including a warranty claim via Digitec). The Legrand support site and support itself is unusable.