Help for writing an app (running zones using Karvonnen method)

Had a run using the app and it works quite well. I have some minor nitpicks and a few ideas:

• 3 digit pulse overdraws on the ring on the right side, so the ring probably needs to be drawn again after the pulse has been updated
  
• The alert screen should show the pulse, that would make it easier to find a maximum without recording. The number on the other page is difficult to read going all out :)
  
• A lock indicator on the Karvonnen page would be nice
  
• Vibration on changing zones could be helpful
  
• Maybe find a way to switch page without unlocking? Since the accelerometer is always active maybe there could be a threshold where you could give the watch a hearty whack to switch while it is not triggered by running/biking?