Starting with Marshmallow, Google included a new hidden settings menu with experimental features. This menu, called the System UI Tuner, is a great way to access tools that may not be quite ready to be called “stable,” but are an excellent way to get eyes on possible upcoming features.
It’s worth noting that third-party manufacturers are free to disable this menu on their custom builds of Android, so it may not be available on your particular device. For example, Samsung and LG both disable this menu, so you can’t access it on any of their non-Nexus devices.
Enabling the System UI Tuner is incredibly easy on supported phones, though: just pull down the notification shade twice (to expose the Quick Settings menu), then press and hold the cog icon for a few seconds. It will begin to spin, then a little wrench icon will appear next to it—this is your indicator that the System UI Tuner has been enabled.
To check it out, scroll all the way down to the bottom of the Settings menu. Depending on what version of Android you’re using, “System UI Tuner” will either be the last or next-to-last option in this menu.
The contents of the UI Tuner will vary depending on what version of Android you’re running. For example, Marshmallow has a toggle for “Show embedded battery percentage,” where this option is found in the “Status Bar” section on Nougat.
Poke around in this menu for a while—there are some really cool feature tucked away in here, especially in Nougat. Go exploring!