Add alert Button in your asp.Net web page when process has been completed.

protected void Button1_Click(object sender, EventArgs e)
{

// Place the following code at the very end

string strMessage = "Process Complete";

string strScript = "<script language=JavaScript>";
strScript = (strScript + ("alert(\"" + (strMessage + "\");")));
strScript += "</script>";
if (!ClientScript.IsStartupScriptRegistered("clientScript"))
{
ClientScript.RegisterStartupScript(this.GetType(), "clientScript", strScript);
}

}