When developing an app, it is sometimes useful to force-quit an application without having to re-start the entire device.
On my iPhone, I can force-quit the active app by double-clicking the home button and swiping the app to the top.
For the actual Apple Watch (not the simulators), force-quitting an app is particularly useful since there are sometimes connection problems between Xcode and the watch app. Also, sometimes I would like to force-quit my Apple Watch app when it is not connected to Xcode.
So, how can I force-quit / terminate the active app on the Apple Watch without restarting the entire device?
When the app that you would like to terminate is open:
- Press and hold the side button and wait until the shut down screen appear. Then let go of the side button.
- Press and hold the side button again until the home screen appears.
Your formerly active app has now been terminated.
PS: The side button is the button below the Digital Crown.
来源：https://stackoverflow.com/questions/30257655/how-do-i-force-quit-an-individual-app-on-an-actual-apple-watch-not-in-the-simul