To start with make sure you have a latest version of the Yosemite (10.10.3 or more) installed on the MacBook Pro or the MacBook Air. Next, open the Terminal after having accessed it from Applications/Utilities option. Unplug the MacBook in case it is on charge. Follow this up by copy-pasting the command- defaults write com.apple.PowerChime ChimeOnAllHardware -bool true; open /System/Library/CoreServices/PowerChime.app & into the available Terminal. After this step, press return key. Now try connecting the laptop to the power source. Gear up to hear the 12 incher Macbook sound of chime you so adore.  In order to wash the sound off; enter the command-  defaults write com.apple.PowerChime ChimeOnAllHardware -bool false; killall PowerChime into the Terminal. Read More: 

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Steps To Get The 12 Incher Macbook Chime Tone On Macbook Air Or Pro - 67Steps To Get The 12 Incher Macbook Chime Tone On Macbook Air Or Pro - 6Steps To Get The 12 Incher Macbook Chime Tone On Macbook Air Or Pro - 23