Monitor activites to complete designated tasks?

The project that i am currently working on will continuously run in the background and will monitor everything the user does without saving it (so that it will not come across as a malicious program). While monitoring the tasks, it will need to give an alert when a certain predetermined task has been completed. So say that i want an alert to pop up when a person searches a certain phrase on google, but I only want it to pop up one time and then never show up again. I was wondering if anyone could help me with the coding for the monitor and detecting part of that, as well as the code that will set the tasks that need to be completed in order for the alert to pop up. Its basically a program that will give you an award if you complete a task successfully.