While the "Double Tap to wake up" feature is getting a common way to wake up the Android devices, Samsung used the Air Wake Up feature on the Galaxy Note 4, so you can wave to wake Note4 up.
To enable Air Wake Up on Galaxy Note 4, do as follows:
1. open Settings and go to the Personalization tab
2. Go to the Accessibility settings, and tap to open the Dexterity and interaction settings
3. Under the Dexterity settings, tap the Air wake up settings and make sure to turn the feature on
4. Now, all it takes to turn the screen of your Galaxy Notye 4 is just moving your hand above the device (to be precise, wave your hand over the sensor right to the speaker at the top panel)