How can you tell if someone is online on Gmail?

Related questions

1. What are Hangouts in Gmail?
2. When you block someone on Hangouts what do they see?
3. Does Google Hangout show on phone bill?
4. Can you Google Hangout with multiple people?
5. Can an Android be hacked?
6. How many users does a video conference on Hangouts support?
7. Can you get hacked by opening an email?
8. Is Gmail getting shut down?
9. Will hangouts be discontinued?
10. Do you need a phone number to use Google Hangouts?

Tags

1. #click
2. #profile
3. #typing
4. #online
5. #check
6. #search
7. #bottom
8. #field
9. #start
10. #person
11. #doesn
12. #green
13. #friend
14. #toward
15. #moment
16. #present
17. #image
18. #right