To make it clear, if your smartwatch has an option to integrated with Bixby voice assistance, then it can be used. You can easily use this feature by setting up Bixby on your phone to the smartwatch. For your information, all models of smartwatches that are compatible with Galaxy Note 4 have integrated Bixby voice usage option. And, you can get Bixby commanding option by pressing on the home key 2 times. Another way to find this voice command feature by saying ‘Hi Bixby