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The Key Combinations Table Of Keychron K2

fn + Keys

KeysFunction
fn + -RGB Speed Decrease
fn + =RGB Speed Increase
fn + 1Select Bluetooth device #1
fn + 2Select Bluetooth device #2
fn + 3Select Bluetooth device #3
fn + 1 (long press for 3s)Pair with Bluetooth device #1
fn + 2 (long press for 3s)Pair with Bluetooth device #2
fn + 3 (long press for 3s)Pair with Bluetooth device #3
fn + Light Effect KeyTurn On / Off the Backlight 
fn + Right ArrowChange The Backlight Color
fn + Left ArrowChange The Backlight Color
fn + delInsert
fn + F1 (Mac mode)F1
fn + F2 (Mac mode)F2
fn + F3 (Mac mode)F3
fn + F4 (Mac mode)F4
fn + F5 (Mac mode)F5
fn + F6 (Mac mode)F6
fn + F7 (Mac mode)F7
fn + F8 (Mac mode)F8
fn + F9 (Mac mode)F9
fn + F10 (Mac mode)F10
fn + F11 (Mac mode)F11
fn + F12 (Mac mode)F12
fn + F1 (Windows mode)Screen Brightness Down
fn + F2 (Windows mode)Screen Brightness Up
fn + F3 (Windows mode)Launches Mission Control
fn + F4 (Windows mode)Launchpad
fn + F5 (Windows mode)Keyboard Backlight Down
fn + F6 (Windows mode)Keyboard Backlight Up
fn + F7 (Windows mode)Rewind
fn + F8 (Windows mode)Play / Pause
fn + F9 (Windows mode)Fast Forward
fn + F10 (Windows mode)Sound: Volume Mute
fn + F1 1(Windows mode)Sound: Volume Down
fn + F1 2(Windows mode)Sound: Volume Up
fn + Win (Windows mode, long press for 3s)Lock / Unlock the Win Key

More key combinations

KeysFunction
fn + BCheck Battery (Still in Beta, not 100% accurate) 

RGB-Backlight Version
Backlight Red = 0~30% Power
Backlight Blue = 30%~70% Power
Backlight Green = 70%~100% Power

White-Backlight Version
Two Rows Backlight off & the Other On = 0~30% Power
One Row Backlight off & the Other On= 30%~70% Power
All Backlight On = 70%~100% Power

Non-Backlight Version
#1 Backlight Red= 0~30% Power
#1 #2 Backlight Red = 30%~70% Power
#1 #2 #3 Backlight Red = 70%~100% Power
fn+ L + Light Effect Key (long press for 3s)Lock / Unlock the Backlight Effect
fn + S + O (Bluetooth mode, long press for 3s)Disable / Enable the Auto Sleep Mode
fn + S + L + R (Bluetooth mode, long press for 3s)Auto Sleep in 10 Minutes Without Typing
fn + S + L + T (Bluetooth mode, long press for 3s)Auto Sleep in 20 Minutes Without Typing
fn + S + L + Y (Bluetooth mode, long press for 3s)Auto Sleep in 30 Minutes Without Typing
fn + J + Z (long press for 3s)Reset the Keyboard
fn + X + L (Windows mode, long press for 3s)Switch Between Function Keys and Multimedia keys (F1-F12)
fn + K + C (Mac mode, long press for 3s)Switch Between Function Keys and Multimedia Keys (Only works for F5 and F6)
fn + I + D (long press for 3s)Switch Between the Delete Key and the Insert Key