There are different barks, too. There is the steady, rhythmic, "I'm barking to hear my self talk. Life is good." bark. Then there is the rapid, higher pitched, urgent, "What the heck was that sound?!" bark. Mine do both, any given night. They call from room to room with the happy "I'm in here! I'm happy! Are you happy?" barks, but then if some clutz falls to the floor of the cage, they can switch to the "I heard something scarey!" bark.
The joeys do a "I can't reach my mommy!" bark the first few nights that they are in their own cage away from the parents.
And, they all do a "Don't attack, it is just me" sort of yelp when they are heading into a pouch where another glider is already cozy.
And, every single morning at dawn, Razzle does her "I'm going to bed, Mommy! Come say goodnight to me!" bark.
To me, it is like a baby crying. If it isn't your baby, a cry is a cry. If it is your baby, you can tell the difference between a unhappy cry or a pain cry. Same with gliders barking. I can wake up out of a dead sleep for the alarm bark, but sleep right through the happy barks.