There is a very simple trick to check whether your friend is invisible or offline in gmail  or gtalk .In gmail or gtalk  open the chat window for the person whom you want to check the status.In gtalk Click the down arrow in the top right corner.

If you are using the Gmail’s inbuilt chat facility, then simply click on the Video & more link in the lower left corner of the chat widget and click on Go off the record.

This will open a menu,select “Go off the record”.Then  type a message for your friend in the chat window and press enter.If a red message saying ‘This person is curently offline and cant receive your messages right now.’,this means that your friend is really offline.If you didn’t get such a message,then it is clear that your friend is online.

How  it works?

By default,the chat history is stored in gmail.If we are selecting  “Go off the record”,it means that we are disabling the storing of chat history for the current chat session.So if the person is not online,it will throw the error message ‘This person is curently offline and cant receive your messages right now.’