Execute code on Browser (Page) Close in ASP.Net

This following code should run only on when page is unload or unexpected close or close window / tab, but right now it is firing on when page it load instead of Unload page.

I have to fire some event when page is closed or browser is closed !!

Code Behind :

Partial Class test
    Inherits System.Web.UI.Page
    Dim dbconn As Object = New DBConnection()
    Private Sub test_Unload(sender As Object, e As EventArgs) Handles Me.Unload
        dbconn.OpenConnection()
        Dim cmd As SqlCommand = New SqlCommand("UPDATE test SET abc = '2' where sno = '123'", dbconn.con)
        cmd.CommandType = CommandType.Text
        cmd.ExecuteNonQuery()
        dbconn.CloseConnection()
    End Sub
End Class