Is there an HowTo for something like that?
I wrote the Company an E-Mail but the have some Holiday (?!) and dont answer soon.
Do you have an idea how the Wifi Version could work? I cant believe its possible to connect it with my upcomming Hotspot System.
BLE tends to be easier to decode than something like Wifi. BLE has a standard method for listing "services" and characteristics. A characteristic could be a single value (like heart rate, oxygenation level etc) but typically manufacturers will just send a whole "packet" of data instead and break it apart in their app. Still if you look at their app, see the values that it's reporting, then use a generic app like "LightBlue" or "NRF Connect" to see the actual data transmitted, it's often easy to see how the values are encoded.
Wifi tends to be much more hassle, as there will be some process to connect the device to your router (many schemes for doing that) and then it will be set to send the data to the manufacturer's server, so intercepting it would need spoofing the DNS requests and setting up a proxy server / wireshark to listen in on the data being sent.