Add the count of unread messages to the page title.
Slack shows an asterisk whenever a new message is received on any of the channels you're on.
When I'm on a different tab (which is most of the time), I don't know if my team is talking about something or not. This feature adds a small counter on the title so that you know how many unread messages you have on the channel you're on. If there are messages on other channels, the title won't change.