If using iPhone, when plugging the charger in, you will hear a sound and the device gets vibrated to signal the user that the machine is being charged. Interestingly, we can make MacBooks sound when charger is plugged in by a command line through Terminal in OS X.
I am not sure if my tip works only in OS X Yosemite.
Launch Terminal (Launchpad –> Utilities). Copy and paste the following code and Enter.
defaults write com.apple.PowerChime ChimeOnAllHardware -bool true; open /System/Library/CoreServices/PowerChime.app &