TrashMe has a function for automatic detection of applications that you put in the Trash in Mac OS X: "Smart detection". When placing an application to the Trash, TrashMe gets opened and offers to delete all files related to the trashed application.
If you move a protected application to the Trash (see Protect applications topic), TrashMe will show an alert box and will propose either to put back the application, or to proceed deletion.
Open TrashMe Preferences
Go to 'Detection' tab
Click on the 'Enable' button