如何在浏览器关闭时清除设计会话？

I am using 'devise' for password authentication in my ruby on rails app. Once I successfully login and I close my browser and open a new browser window I am still logged in. Lets say I am using Chrome, I close all instances of chrome and then open a new one. I am still logged in. The same is the case when I am doing IE and Firefox too.I am using 'devise' for password authentication