Who can see me 'online'?
The same people who can see your last seen time can see when you are online. It is one setting, not two, and it is under Settings, Privacy and Security.
The exceptions, and why they exist
Regardless of your setting, people will see you online for a brief period, about 30 seconds, if you have just interacted with them. Specifically:
- You send them a message in a one-to-one chat.
- You send a message in a group you are both in.
- You read a message they sent you in a one-to-one chat.
These are cases where being hidden would be transparently false. Somebody who has just received a reply from you knows you are there; pretending otherwise would make the indicator unreliable for everyone rather than private for you.
Setting it
- Open Settings, then Privacy and Security.
- Choose Last Seen and Online.
- Pick Everybody, My Contacts or Nobody, and add exceptions if you want.
Remember the reciprocity rule
Hiding your status from someone means you cannot see theirs. You will see an approximate last seen value instead, which tells you whether they are broadly reachable without revealing a pattern. There is no configuration in which you watch others while staying invisible yourself.