Setting the Alarm Clock's Bluetooth volume
You need to adjust the volume of the alarm once you connect your BT speakers. In Android, the volume of audio is determined by two mostly orthogonal things: the first is the type of the audio (it's called stream type), so you have separate volume settings for media, ringtones, alarms, etc; the second is the kind of the output device: built-in speaker, headphones, BT headset, USB, etc.

You might have noticed that media volume for the phone speaker and headphones is controlled separately. The same thing is for BT sound output.