You don't want to make yourself visible to rest of your friend, with the help of following steps you can be logged in to Gmail Chat and see if your contacts are online, but they won’t be able to see you’re online.
1.) Start a new chat with the intended user.
2.) Set the chat to off the record so that it doesn’t get logged to the gmail account.
3.) Send a message to the user. If the user is online and invisible, the message will be delivered.
4.) If the user is offline, you will get an error message indicating that the user is offline.