The Apple Watch will ONLY play music via Bluetooth device paired to the Apple Watch. Bluetooth Headphones or Bluetooth speakers.
The Apple Watch will Not play music via the Apple Watch speakers (takes too much power from the tiny Apple Watch battery).
I have successfully paired 4 different Bluetooth headphones to my Apple Watch. The Most Difficult part is finding the headphone instructions on how to put them into "Discovery" mode so that the Apple Watch can see and pair to the headphones.
- Sony Noise Canceling headphones
- Apple AirPods (the easiest, as there is a pairing button on the back of the case)
- a pair of Jabra 15 year old Bluetooth headphones
- another 15 year old Bluetooth headphones, that I forget the name of at the moment).