Level 2
You can do with JavaScript. Please see the following links.
http://stackoverflow.com/questions/23690666/check-if-my-website-is-open-in-another-tab http://stackoverflow.com/questions/13779508/open-url-in-new-tab-or-reuse-existing-one-whenever-possible http://stackoverflow.com/questions/13425440/check-if-a-browser-tab-is-already-open-so-i-dont-make-extra-tabs
