Alert Message from Code behind with ASP.Net and C.Net

public static void ShowAlertMessage(string message)
{
Page page = HttpContext.Current.Handler as Page;
if (page != null)
{
ScriptManager.RegisterStartupScript(page, page.GetType(), "err_msg", "alert('" + message + "');", true);
}
}

Here, "err_msg" unique key value for alert message. It is your wish .