The BLE MAC address consists of a random periodically changing part and a deterministically generated part based off encrypting the random part with a device-sp

The BLE MAC address consists of a random periodically changing part and a deterministically generated part based off encrypting the random part with a device-specific secret key (the Identity Resolving Key). This allows paired devices to identify the BLE advertiser since they know the IRK, while random devices like signs would not know the IRK and thus would not be able to deanonymize the MAC address. This feature is called Resolvable Private Addresses (RPA).