Displaying users online in the backend

I can’t seem to be able to find a plugin that does this, but only for the backend! I need to know which users (only 8) are online and possibly editing content, because I’m the one maintaining the website and I don’t want content to get lost while I’m working on the website and someone else is editing a post. So I need to know if someone is online before I start my work.

The plugins I found were all about the front end.