Identify if a user is online in Google Hangout
Hangouts doesn’t use the green or grey dots that Google Talk used to identify if someone is online or offline. Instead, you can tell if a contact is online or not  if their profile picture is clear or faded. A faded profile picture means your contact is unavailable, and a clear picture means they’re online. One downside is that Hangouts doesn’t support the “invisible” status like Google Talk did