Most Nokia Lumia devices come with double tap to wake up functionality but it does not work as expected in the Nokia’s Android phones, X and XL. The reason is X and XL use Vibrator and Accelerometer to implement Double Tap on these devices.
This is same for the Nokia 5XX series so it does not work as expected. You must tap really hard and at other times even hitting the phone at its back would wake it up.
Nokia did this to reduce wastage of battery, the screen was not used to implement this feature.