Know if a contact is online from PC, from mobile or offline.
With the old XMPP connection it's still possible to know if someone is online and what app he's using with this combinations:
-XMPP online/away
-from PC online/away
-from mobile
*Unfortunally at the moment it's impossible to know if someone is online or offline from mobile*
*It's not a chat client!*
No personal datas are collected using this application.
Sources are avaiable on github
https://github.com/monossido/Hangout-isOnline with GPLv3 license
**Hangouts isOnline is not affiliated to Google**