docs: def send_key(self, key):
          """ Send a key to the Horizon box. """
          cmd = struct.pack(">BBBBBBH", 4, 1, 0, 0, 0, 0, key)
          self.con.send(cmd)
  
          cmd = struct.pack(">BBBBBBH", 4, 0, 0, 0, 0, 0, key)
          self.con.send(cmd)