NotifyVisitors - Notification Management Software for shopify enables you to show notifications when it matters based on visitor behaviour. Select from multiple targeting rules including visitor duration or frequency, browser or device type, url source, time of the day and many more.
You can install the app from here : http://apps.shopify.com/notifyvisitors-notification-management-software
To learn more about NotifyVisitors, visit http://www.notifyvisitors.com/