How to get the BTHome encryption key for Shelly H&T (Home Assistant)

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.

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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.

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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.