Problem overview
When using a Shelly H&T in BTHome (BLE) mode with encryption enabled, Home Assistant requires the 128-bit (32-character hexadecimal) encryption key.
However:
- The Shelly mobile app does not display this key
- The 6-digit PIN shown in the app is NOT the BTHome encryption key
- The key cannot be derived from the PIN
As a result, pairing an encrypted BTHome Shelly H&T seems impossible at first.
The solution: Shelly BLE Debug app
Shelly provides a separate utility app called Shelly BLE Debug that reveals the BTHome encryption (bind) keybroadcast by the device.
Important notes about BTHome encryption
- BTHome supports both encrypted and non-encrypted modes
- Apps like Home Assistant accept both
- Encryption is optional, not mandatory
- Currently Home Assistant does not warn on encryption downgrade. It should be solved shortly: https://github.com/home-assistant/core/pull/159646
- Shelly BLU TRV devices cannot be encrypted (BTHome used to report temperatures); in addition, if you use an external Shelly sensor (eg. Shelly H&T), it could not be encrypted.