Question about Netatmo Smarter smoke detector set of 3

The smoke detector does not require a subscription (all Netatmo products work without a subscription), but a free Netatmo account can be set up to receive smartphone notifications and to connect the smoke detector to Wi-Fi. However, the smoke detector will also work on its own without any Wi-Fi installation, in which case it is simply not 'Smart', meaning that no notifications will be sent to your mobile devices.

Yes, but this is (currently) free of charge.
I don't know the details of the interface, but I assume that the smoke detector sends the information via WLAN connection to a Netatmo server, which in turn sends the alarm to the smartphone. (Configuration of the smoke detector / mobile numbers via Netatmo login).

https://www.netatmo.com/de-ch...

Free App / No subscription fees / App available in App Store / Google Play / Free online access to your Smart Smoke Detector