The vibration notifications feature discreetly alerts you that your baby is awake. Especially in the background e.g. when you turn off the LCD by using sleep button or whenever you run another application on the screen.
Here are guides for respective operating systems:
1. Before you start monitoring, click on the menu(top right corner) on the parent station.
2. Select advanced
[iOS]
3. Turn on/off Vibrate when noisy
[Android]
2. Turn on/off Vibrate in background