Thanks for catching this. The iOS app is currently blocked in Germany (and some other EU countries) because DSA information is still pending. Hopefully soon. Android is available there. The biofeedback can be accessed via browser without creating an account. The link and details are in the repo README.

Tried it on website but I always get Signal too weak, even if I breathe heavily, in an otherwise silent room. iPhone 13mini.

Great feedback, thank you. The browser version still depends on the device/browser mic chain and it looks like the threshold is too strict on some iPhone/Safari setups. I`ll look into this case. It should not get stuck at signal too weak if the room is silent and breathing clearly audible.