If you use Chrome browser, you could enable desktop notifications for your exotel calls. 

1) Login to exotel. The next time you get a call, you will see a popup like this: 

2) Click on "Get Desktop Notifications?" link in that popup. Chrome will ask you if you wanna "Allow" exotel to notify you through it's desktop notification framework like this:

3) And that is it. Now whenever you get a call, irrespective of which window you are on, you will always be alerted. Here, I am looking into my terminal yet get the notification.