how to know who is online although you are off line?

this is a new explication to know who's online from your friends although you are offline.
A very simple way is a Facebook application Online Now that allows you to do so.

Firstly, enter on the application link, and then click the Access the application.

Then allow the application to know friends online,then click on allow.

Then you can directly to know your friends online although you are off line.

Thank you very much for Following;)