The System UI Tuner option of Android N changes a couple of things from Marshmallow. We've already covered how you can use it to tweak your status bar and calibrate the color of your screen, but there's another aspect that it lets you modify and that's the Do not disturb (DND) mode.

Two settings can be changed for DND in the System UI Tuner: Show with volume buttons and Volume buttons shortcut. The first one will always show a DND toggle each time you change your volume, allowing you to quickly set DND on or off.

The second option is a more subtle way of activating DND by using the volume buttons on your device. You simply go to the lowest volume, then you press again and DND gets triggered telling you with a visual cue that only alarms will sound from now until you turn off DND. You can tap End now to deactivate DND or press the volume up button for the same effect.

If both of these options are deactivated in System UI Tuner, the only way of turning on DND is to use the Quick Settings toggle, provided you have enabled it to show up.