If someone has the last-seen setting on, you’ll notice a timestamp beneath their name in the conversation window, indicating when they were actively using Hangouts through Gmail, web, or phone app.
Here’s how to tell whether individuals are online in Google Hangouts. You can get a few indications about a user’s status using the Google Chrome Hangouts Plugin for Windows. A green dot will appear next to the icon of people who are active on the internet and offline. The friend list does not show any indication when users are offline.
Tap the contacts icon in the lower-left corner. You’ll see a list of contacts who are “On Hangouts” and “Not on Hangouts” there.
When Hangouts members check their Hangout, they’ll see a notification and be able to read your message. You’ll be able to recognize who has read your message since the new Hangouts displays the user’s profile picture below the most recent message they’ve seen in a discussion stream.
You are active in Hangouts if you are automatically signed into Hangouts when you sign into Gmail.
