Unlike Word or Excel, Access does not warn you when data is changed. Unless you make a structural or code change, Access thinks you know what you want to know and allows you to enter or change data and the close the application without a squeak.
There is a way around this:
"In Microsoft Office Access 2007, by default, users are not prompted to confirm changes after modifying and saving records on a form. But often you might want to prompt users to confirm their changes before the record is saved.
You can use a BeforeUpdate event procedure to display a confirmation prompt and handle a user's response to either cancel or continue with the save.
This visual how-to topic illustrates how to display a custom dialog box to prompt users to cancel or continue with saving changes to a record.