On="1" and Off="2" within one click

Question

I'm using one button for "on and "off" in asp.net c#. When i click that button it is "on" and when i click that same button second time it is "off". Now i want to do this within one click. This means that once i click and hold that button it should be "on" till i release the button, when released it should be "off". Please let me know how can i do that !

 

protected void Page_Load(object sender, EventArgs e)
    {
        ardo = new SerialPort();
        ardo.PortName = "COM5";
        ardo.BaudRate = 9600;
    }
    protected void BlueOn(object sender, EventArgs e)
    {
        if(Session["currentState"] == null)
           Session["currentState"] = "2";

       if(Session["currentState"].ToString() == "1")
         {

            Session["currentState"]= "2";
         }
         else
         {

            Session["currentState"]= "1";
         }
        ardo.Open();
        ardo.Write(Session["currentState"].ToString());
        ardo.Close();

    }