Hi
If the earphones are already paired with any other devices (for example, your iPhone), it may help to unpair them first:
- On your iPhone, go to: Settings > Bluetooth > tap the info icon "i" next to your earphones > tap to Forget this Device.
When Wrist Detection and a passcode are enabled, your watch will lock automatically when it is removed (or when it thinks it has been removed) from your wrist. This will also cause the Workout app to pause.
A loose fitting band can trigger this by allowing your watch to lift from your wrist and/or by allowing clothing (for example, the end of a sleeve) to slip beneath the back of the watch.
During exercise, Apple Watch should be worn snugly on the top of your wrist. Apple suggests that you consider tightening your band before workouts and loosening it again afterwards. Better contact with your wrist may also improve heart rate sensor performance during your workout.