Public Function IsACCDE() As Boolean
    ' This property exists only in compiled DBs (.mde, .accde)!
    On Error Resume Next
    IsACCDE = (CurrentDb.Properties("MDE") = "T")
End Function

This code returns True if MS Access has been saved as ACCDE and False it it has not. This is different than the built in IsCompilled() function that return True or False based on the actual code being compiled or not.