If you want your app to respond to the user shaking the phone, then you need to follow these instructions:

1. In Config.XML, enable shaking detection:
   <Device.System.DetectShaking>true</Device.System.DetectShaking>
2. On the Zebble page or module that should respond to Shaking, add an event handler in the OnInitializing event:

   public override async Task OnInitializing()
   {
           await base.OnInitializing();
           // ....
           Device.Accelerometer.DeviceShaken.Handle(OnDeviceShaken);        
   }

3. Add the event handler:

   Task OnDeviceShaken()
   {
       return Alert.Show("TADA! You device was shaken!");
   }

4. Remove the handler when your page or module is disposed:

   public override void Dispose()
   {
       Device.Accelerometer.DeviceShaken.RemoveHandler(OnDeviceShaken);
       base.Dispose();
   }

Testing on Windows

To test the shake functionality on Windows (dev time) launch the inspector by pressing the Ctrl + Click on any element.

The on the top bar, click on the Shake icon.