How can I tell if someone is online on Google Hangouts?

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Tags

1. #windows
2. #active
3. #chrome
4. #hangouts
5. #people
6. #plugin
7. #indicator
8. #google
9. #offline
10. #using
11. #online
12. #status
13. #friend
14. #indicators
15. #green
16. #users
17. #their