How to make the subscriptions module produce notifications on a screen?
Same thing I wanted to do for some kind of notification.
Finally, this was the implementation:


Added one function which returns the count and notification with HTML.
Then added Ajax request to fetch the result and place it on the notification element which is already placed in page.tpl.php
Added JS code to custom.js which works on every page of site.
See below:





But remember don't make it heavy ajax request, it may slow down your site. And remember to add JS code at bottom of page.
Also you can do one thing, put ajax request on click of the element, look what StackExchage do:





on click of notification they send request and fetch the data...